0. Clark West, MD #{149} Stuart E. Mirvis, MD #{149} Kathirkamanathan Shanmuganathan, MD Transsphenoid Basilar Skull Fracture: CT Patterns’ 329 Neuroradiology The authors studied computed tomo- graphic (CT) scans obtained in 40 patients with transsphenoid basilar skull fractures to establish if there were reproducible patterns of frac- hire along lines of weakness. Medical records were reviewed. Four major fracture patterns were identified: an- tenor transverse (n = 22), lateral fron- tal diagonal (n = 7), posterior trans- verse (n = 16), and mastoid diagonal (n 3). Eight patients had two frac- ture patterns. Eleven of 40 patients (28%) died as a result of their head injury. The diagonal patterns were statistically significantly more fre- quently associated with in-hospital mortality than were the transverse fractures (P = .014). Complications included blindness, cranial nerve in- jury, cerebrospinal fluid leak, and hearing loss. These results indicate that transsphenoid basilar skull frac- hires occur along reproducible lines of weakness, including a coronal plane through the anterior sphenoid body and pterygoid plates, a coronal plane through the posterior sphenoid body and clivus, and the sphenope- trosal synchondrosis. Index terms: Head, injuries, 12.41 #{149} Skull, fractures, 12.41 #{149} Sphenoid bone, 123.41, 124.41 Radiology 1993; 188:329-338 ‘From the Department of Diagnostic Radiol- ogy, University of Maryland Medical Center, 22 S Greene St. Baltimore, MD 21201 (O.C.W., S.E.M., KS.) and the Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Mo (O.C.W.). Received Janu- ary 8, 1993; revision requested February 16; revi- sion received March 23; accepted March 25. Ad- dress reprint requests to S.E.M. RSNA, 1993 F RACTURES of the skull base have been increasingly recognized as frequent injuries in patients with seri- ous head trauma. In one study before the era of computed tomography (CT), 19% of 1,097 patients with skull fracture had fractures of the skull base (1). Recent literature suggests that sphenoid bone fractures are the most common skull fractures, occurring more frequently than fractures of the temporal bone and the cranial vault in patients evaluated with CT because of blunt head trauma (2). Previous diagnostic imaging literature has fo- cused on fractures of single bones or on single regions of the skull base (2- 13). To the authors’ knowledge, no pre- vious publications in the imaging lit- erature have described the complete course of fractures as they extend across the entire skull base as de- picted with CT. Since 1985, we have periodically encountered examples of complex basilar skull fractures that have occurred primarily as the result of lateral impacts to the head. We noted that the fractures seemed to follow one of a few typical patterns. To establish if there were reproduc- ible patterns of skull base fracture and to establish the lines of weakness through which these fractures pass, we reviewed our previously identi- fled cases. Only fractures extending across the entire skull base from one side to the other and crossing the sphenoid body along their course were included in the study. MATERIALS AND METHODS Review of Pertinent Anatomic Features of the Skull Base To better understand the patterns of skull base fractures, it is helpful to review certain anatomic features of this complex region. Important anatomic landmarks on the internal surface of the skull are shown in Figure 1, and Figure 2 diagrams the rel- evant CT anatomy. The sphenotemporal buttress is formed at the junction of the orbital surface of the greater wing of the sphenoid bone and squamous portion of the temporal bone (7). It corresponds to the innominate line seen at plain radiography. The articulation between the posterior margin of the greater wing of the sphe- noid bone and the petrous portion of the temporal bone is an important pathway for fractures. The bones are joined by a fibrocartilaginous band. Medially, this band is broad and is termed the foramen lacerum. The foramen lacerum is located at the base of the medial pterygoid plate and is bounded by the sphenoid body and clivus, medially; the greater wing, antero- laterally; and the petrous apex, posteri- orly. Laterally, the fibrocartilaginous band thins and extends from the foramen lace- rum to the sphenoid spine as the spheno- petrosal synchondrosis. Both the foramen ovale and the foramen spinosum are lo- cated immediately anterior to the spheno- petrosal synchondrosis, with the foramen spinosum indicating the lateral extent of the synchondrosis. The cartilaginous audi- tory (eustachian) tube runs a course paral- lel and directly inferior to the synchondro- sis. The carotid canal is adjacent to the posterior margin of both the sphenopetro- sal synchondrosis and the foramen lace- rum along the endocranial aspect of the skull base. The posterior margin of the petrous portion of the temporal bone is another fracture pathway and is bounded medially by the petrooccipital fissure, which ex- tends from the foramen lacerum to the jugular foramen. Beyond the jugular fora- men, the temporal and occipital bones join at the occipitomastoid suture (14,15). Patients For the period from June 1985 through June 1992, our trauma radiology data base of 4,229 patients was searched for patients classified as having complex fractures of the skull base, clivus, or sphenoid bone. Abbreviations: AT = anterior transverse, CN = cranial nerve, CSF = cerebrospinal fluid, LFD = lateral frontal diagonal, MD = mastoid diagonal, PT = posterior transverse.
Transcript
0. Clark West, MD #{149}Stuart E. Mirvis, MD #{149}Kathirkamanathan Shanmuganathan, MD
Transsphenoid Basilar Skull Fracture:CT Patterns’
329
Neuroradiology
The authors studied computed tomo-graphic (CT) scans obtained in 40patients with transsphenoid basilarskull fractures to establish if therewere reproducible patterns of frac-hire along lines of weakness. Medicalrecords were reviewed. Four majorfracture patterns were identified: an-tenor transverse (n = 22), lateral fron-tal diagonal (n = 7), posterior trans-verse (n = 16), and mastoid diagonal(n 3). Eight patients had two frac-ture patterns. Eleven of 40 patients(28%) died as a result of their headinjury. The diagonal patterns werestatistically significantly more fre-quently associated with in-hospitalmortality than were the transversefractures (P = .014). Complicationsincluded blindness, cranial nerve in-jury, cerebrospinal fluid leak, andhearing loss. These results indicatethat transsphenoid basilar skull frac-hires occur along reproducible linesof weakness, including a coronalplane through the anterior sphenoidbody and pterygoid plates, a coronalplane through the posterior sphenoidbody and clivus, and the sphenope-trosal synchondrosis.
‘From the Department of Diagnostic Radiol-ogy, University of Maryland Medical Center, 22S Greene St. Baltimore, MD 21201 (O.C.W.,S.E.M., KS.) and the Mallinckrodt Institute of
Radiology, Washington University School ofMedicine, St Louis, Mo (O.C.W.). Received Janu-ary 8, 1993; revision requested February 16; revi-sion received March 23; accepted March 25. Ad-dress reprint requests to S.E.M.
� RSNA, 1993
F RACTURES of the skull base havebeen increasingly recognized as
frequent injuries in patients with seri-ous head trauma. In one study before
the era of computed tomography(CT), 19% of 1,097 patients with skullfracture had fractures of the skull base
(1). Recent literature suggests thatsphenoid bone fractures are the mostcommon skull fractures, occurringmore frequently than fractures of thetemporal bone and the cranial vaultin patients evaluated with CT because
of blunt head trauma (2). Previousdiagnostic imaging literature has fo-
cused on fractures of single bones or
on single regions of the skull base (2-13).
To the authors’ knowledge, no pre-vious publications in the imaging lit-
erature have described the completecourse of fractures as they extend
across the entire skull base as de-picted with CT. Since 1985, we have
periodically encountered examples of
complex basilar skull fractures thathave occurred primarily as the resultof lateral impacts to the head. Wenoted that the fractures seemed tofollow one of a few typical patterns.To establish if there were reproduc-ible patterns of skull base fracture and
to establish the lines of weaknessthrough which these fractures pass,
we reviewed our previously identi-fled cases. Only fractures extendingacross the entire skull base from one
side to the other and crossing the
sphenoid body along their coursewere included in the study.
MATERIALS AND METHODS
Review of Pertinent AnatomicFeatures of the Skull Base
To better understand the patterns ofskull base fractures, it is helpful to review
certain anatomic features of this complex
region. Important anatomic landmarks on
the internal surface of the skull are shown
in Figure 1, and Figure 2 diagrams the rel-
evant CT anatomy.
The sphenotemporal buttress is formedat the junction of the orbital surface of thegreater wing of the sphenoid bone andsquamous portion of the temporal bone
(7). It corresponds to the innominate lineseen at plain radiography.
The articulation between the posteriormargin of the greater wing of the sphe-noid bone and the petrous portion of thetemporal bone is an important pathwayfor fractures. The bones are joined by afibrocartilaginous band. Medially, thisband is broad and is termed the foramenlacerum. The foramen lacerum is located
at the base of the medial pterygoid plateand is bounded by the sphenoid body andclivus, medially; the greater wing, antero-
laterally; and the petrous apex, posteri-orly. Laterally, the fibrocartilaginous band
thins and extends from the foramen lace-rum to the sphenoid spine as the spheno-
petrosal synchondrosis. Both the foramenovale and the foramen spinosum are lo-cated immediately anterior to the spheno-petrosal synchondrosis, with the foramenspinosum indicating the lateral extent of
the synchondrosis. The cartilaginous audi-tory (eustachian) tube runs a course paral-
lel and directly inferior to the synchondro-sis. The carotid canal is adjacent to the
posterior margin of both the sphenopetro-
sal synchondrosis and the foramen lace-
rum along the endocranial aspect of theskull base.
The posterior margin of the petrousportion of the temporal bone is anotherfracture pathway and is bounded mediallyby the petrooccipital fissure, which ex-
tends from the foramen lacerum to thejugular foramen. Beyond the jugular fora-
men, the temporal and occipital bones joinat the occipitomastoid suture (14,15).
Patients
For the period from June 1985 throughJune 1992, our trauma radiology data baseof 4,229 patients was searched for patientsclassified as having complex fractures ofthe skull base, clivus, or sphenoid bone.
Orbital surface of frontal bone Cnbsform plate of cthrnosd Fo’,sc
Planum sphenoidale Anterior clins,sd procc�%
lcs’.er wing of sphenoid bone Spheno-’.quams’s.sl suture
Orbital ‘ut-face of greaser wing Foramen lacerurn
Limbos sphenoidale Carotid canal
(ert-bral surface of greaser wing Spheno. pesrosal synchondrosis
Ss�uasn,’u�. portion of temporal bone Petro - occipital fissure
Foramen annIe Clivus
I:oramen spinosum Jugular firamen
l’,sr,’us pi�rsi,in ,‘i icmporal bone OcCipiio - nsasti,id suture
5db lurcica Foramen magnum
l),,r’.uni scllae Occipital hone
Figure 1. Anatomic features of the skull base.
Eihmoid air cells
Orbital surface of frontal bone
Lateral orbital wall
Sphenoiemporal buttress
/ygoinaiic process of temporal bone
Cerebral surface of greaser wing
Mandibular fossa
Tympamc portion of temporal bone
Condylar head of mandible
Ferrous portion of temporal bone
Clivas
Cnsta galli
Planum sphenoidale
Anterior clinoid process
Sphenoid Sinus
Foramen lacerum
External auditory canal
Spheno . petrosal synchondrosis
Caretid canal
Occipiro . mastoid suture
Jugular foramen
Occipital bone
Figure 2. Anatomic features of the skull base at CT. This composite drawing shows relevant
features normally seen at CT by integration of information from several sections.
330 #{149}Radiology August 1993
Fifty-three potential study patients were
identified. The film jackets for 39 of these
patients were available for review. Ofthese, 29 patients had basilar skull frac-
tures traversing the sphenoid body and/or
clivus, nine had fractures lacking the
transsphenoidal component and were ex-
cluded from further study, and one pa-
tient had a technically inadequate study.To this group of 29 patients identified ret-rospectively, we added 11 patients with
similar fractures identified prospectively
from July to September 1992. All patientswere victims of blunt force trauma andwere evaluated in the admitting area ofthe shock and trauma center at the Uni-versity of Maryland Medical Center. Pa-
tients ranged in age from 13 to 58 years
(mean, 31 years) and included 34 men andsix women (male:female ratio, 5.7:1).
At least one head CT scan obtained witha 10-mm section width and photographedat soft-tissue and bone windows wasavailable for each patient. Additional thin-
section (1.5-5-mm section width) examina-
tions emphasizing the facial bones, tempo-
ral bones, or skull base were available in
34 cases. The scanning protocol was based
on patient need and varied with availablescanner technology. Images were obtained
with one of the following CT scanners:9800 Quick, Hi-Lite Advantage (GE Medi-cal Systems, Milwaukee, Wis), DR-H, and
Hi-Q (Siemens Medical Systems, Iselin,NJ). Most patients underwent multiple
follow-up examinations, but only the mi-tial conventional head CT and the firstthin-section examinations were used in
this study.
Each examination was reviewed bythree staff radiologists (S.E.M., KS.,O.C.W.), and the individual fractures wereenumerated by consensus. Pertinent soft-
tissue findings, including scalp swelling
and laceration, were also noted. On thebasis of the CT findings, a judgment as to
the most likely impact site was made. Sub-sequently, the cases were classified into
fracture patterns.Mortality information was available for
all 40 patients. The medical charts of 39 ofthe 40 were available for review but wereincomplete in three cases. Mechanisms ofinjury (motor vehicle accident, assault
with a blunt object, or otherwise), site ofimpact on the basis of physical findings,
patient condition at hospital discharge,and complications related to the basilarskull fracture were recorded. Autopsy re-
ports were available for three patients.
The relationship between mortality and
skull base fracture pattern was determined
by using the Fisher exact test.
RESULTS
Four major patterns of skull basefractures were evident among our 40
patients. These included the anteriortransverse (AT) pattern in 22 patients,
the lateral frontal diagonal (LFD) pat-tern in seven patients, the posteriortransverse (PT) pattern in 16 patients,and the mastoid diagonal (MD) pat-
tern in three patients (Table). Eight
patients had evidence of two majorpatterns, and several variations on the
major patterns were observed.
AT Pattern
The key to the identification of theAT pattern (Figs 3, 4) is the demon-stration of a coronal fracture throughthe sphenoidal plane at the base ofthe anterior clinoid processes. Theexact position across the anteriorsphenoid body varies slightly from
the sphenoidal limbus to the roof ofthe extreme posterior ethmoid aircells. Most fractures pass through theroof of the sphenoid sinus anteriorly.
The fracture typically begins in the
squamous portion of the temporal
bone, courses anteriorly to the sphe-notemporal buttress, and then pro-
ceeds medially along the orbital sur-face (vertical plate) or the anterior
cerebral surface (horizontal plate) of
the sphenoid bone. The fracture inter-sects the sphenoid body at or slightlyposterior to the junction, with theethmoid bone producing the charac-teristic transverse fracture across theposterior aspect of the floor of the an-terior cranial fossa. This coronal frac-ture plane may extend to involve thepterygoid plates as discussed below.
The fracture exits the sphenoid bodythrough a similar pathway involving
Case Details in 40 Patients with Transsphenold Basilar Skull Fractures
Volume 188 #{149}Number 2 Radiology #{149}331
Case No.!Age (y)/Sex Fracture Cause Site of Impact Fracture Pattern Outcome
1/30/M MVA L frontotemporoparietal AT CD, CN 11(i), CSF leak (nose, mouth)2/19/M MVA R temporal AT CD, CN 111(i), R optic sheath hematoma3/46/F Fall from horse R temporal AT CD; CN 11(i), ffl(i)4/23/M MVA R mastoid AT CD, CSF leak (inner ear)5/23/M MVA L lateral frontal, temporal AT oblique CD, �N 111(i)6/38/M Assault with bat L lateral frontal AT CD, CN 11(i), CSF leak (inner ear)7/58/M Assault, blunt L lateral frontal, temporal AT oblique CD
8/40/M9/18/F
MCA (low velocity)Fall from horse
R temporalL temporal
ATAT
GoodCD, CSF leak (inner ear), I-IL(i)
10/23/M Assault, blunt R lateral frontal AT CN 11(1), 111(i); no data on CD11/56/M MCA L lateral frontal, temporal AT, LFD CD, cN 11(i)12/34/M
13/29/M
Missile, blunt
MVARlateral frontalR temporoparietal
AT obliqueAT, PT
Died on day 10; no autopsyCD; CN V(i), V1(i), VI1(c); l-LL(c)
14/17/M MVA L temporal AT, PT CD; CN 11(i), 111(i); CSF leak (nose, ear(cJ); HL(b)15/17/M MVA L lateral frontal, temporal AT, F1� Died on day 4; no autopsy16/34/M MCA L temporal AT, V1 CD
17/19/M MCA L frontotemporal AT, ant sagittal* Died on day 2; no autopsy; CSF leak (nose, ears[bJ)18/25/M Missile, blunt L lateral frontal AT, ant sagittalt Good19/56/M Fall R frontal AT, ant sagiftaP Discharged to home; no additional data
20/18/F MVA L lateral frontal AT, LFD Died on day 7; head autopsy-CN 111(1); CSF leak(nose ears[b]); DI
21/20/M MVA, hit tree L zygoma AT, LFD Died on day 33; meningitis; autopsy: CN VI(c), VII(c);conductive HL(c); no data on CD
40/17/M MVA R mastoid, parietooccipital MD Died on day 1; no autopsy; DI
Note.-ant = anterior,b = both, c = contralateralto site of impact, CD = cognitive deficit, DI = diabetes insipidus, HL = hearingloss, L = left, MCA = mo-torcycle accident, MVA = motor vehicle accident, R - right.
a Associated fracture.
the contralateral greater wing alongthe orbital surface (horizontal plate)or the anterior cerebral surface (verti-cal plate). In severe fractures, the frac-ture will continue to propagate intothe contralateral squamous portion ofthe temporal bone.
Fractures Associated with ATPattern
Several fractures were seen associ-ated with the AT pattern. In the set-ting of temporal impacts, commi-nuted ipsilateral greater sphenoidwing fractures (cases 1, 2, and 17) andipsilateral temporal bone fractures(cases 2, 4, 6, and 9) were noted. Thelatter group excludes patients withconcomitant PT and LFD fracture pat-tents who had temporal bone frac-tures by definition.
In cases where the impact wassomewhat more anterior, in the lat-eral frontal region or the malar emi-nence of the face, additional ipsilat-eral orbital roof fractures occurred ineight of 22 patients (cases 1, 2, 4-6, 9,18, and 20). The contralateral orbitalroof was also fractured in four pa-tients of this group (cases 4, 10, 16,and 22). Fractures of the zygomatico-maxillary complex were associatedwith the AT pattern in eight cases(cases 5, 6, 8, 11, 17, and 20-22), while
simple zygoma fractures were seen onthe ipsilateral side of the impact infour additional cases (cases 2, 7, 13,and 14). One contralateral simple zy-goma fracture was also seen (case 6).The orbital apex is in proximity to theAT fracture plane in all cases. Sub-stantial comminution near the orbitalapex occurred in nine cases (cases 1, 2,
5, 6, 8, 11, 14, 15, and 20) (Fig 5). Thepterygoid plates were fractured in
four patients with the AT pattern,without signs of Le Fort midface frac-tures (cases 2, 7, 13, and 14).
Variants of the AT Pattern
In three of 22 patients with the ATpattern with anterolateral impact,(cases 5, 7, and 12), there was anoblique component within the majorfracture pattern. The force appearedto be transmitted along the ipsilaterallateral orbital wall and through thesphenotemporal buttress to the sphe-noid body (Fig 6). The sphenoid boneis fractured along the anterior trans-
verse plane, and the fracture thencourses slightly posteriorly andobliquely along the posterior portionof the cerebral surface of the greater
332 #{149}Radiology August 1993
sphenoid wing. The fracture course
across the sphenoid body is clearly
more anterior than the course ob-
served in the lateral frontal diagonal
pattern and does not enter the sphe-nopetrosal synchondrosis as occurs in
the LFD fracture as described below.Thus, this slightly oblique fracture
plane is best considered a variant ofthe anterior transverse pattern, sinceit crosses the sphenoid body in this
plane.In five of the 22 patients with AT
patterns (cases 13-16 and 22) with
slightly more posterior temporal im-
pacts, there was an associated PT frac-
ture pattern.
Impacts in the frontal bone onlyslightly lateral to the midline pro-
duced a sagittal fracture through theethmoid air cells. In three cases (cases17-19), such a sagittal plane fractureintersected the coronal AT pattern,forming a T in the anterior sphenoidbone.
LFD Pattern
The LFD fracture pattern occurs asthe result of impact to the lateral fron-tal region or the anterior malar emi-nence and was observed in seven pa-tients of this study (Figs 7-9). Forceappears to be transmitted along the
lateral orbital and/or lateral maxillary
sinus wall to the sphenotemporal but-tress. The lateral maxillary sinus wasfractured in six of six cases (cases 11,20, 21, 23, 24, and 26) where it couldbe seen, and the lateral orbital wallwas fractured in four of seven cases
(cases 20, 23, 25, and 26). From the
sphenotemporal buttress, the force istransmitted along the ipsilateral sphe-noid sinus wall to the posterior wall
of the sphenoid sinus. The fracturecrossed the sphenoid body in a trans-verse plane in five of the seven pa-
tients (cases 11, 21, 23, 24, and 26) and
crossed the sphenoid body diagonally
in the two other patients (cases 20and 25). The fracture continues
through or immediately anterior tothe contralateral carotid canal into thesphenopetrosal synchondrosis. The
fracture may then continue throughthe tympanic portion of the temporalbone as seen in two of the seven cases(cases 11 and 26) or may continue
more posteriorly into the petrous por-tion of the temporal bone, which wasobserved in three cases (cases 20, 21,
and 24). In the remaining two pa-
tients, there were fractures in both thetympanic and petrous portions (cases
23 and 25).
Fractures Associated with the LFDPattern
Pterygoid plate fractures on the
side of impact were present in five ofsix cases of the LFD pattern in whichthe pterygoids were scanned (cases11, 20, 21, 23, and 24). There was anassociated zygomatic fracture in fiveof six patients (cases 11, 20, 21, 23,
and 26) in whom the zygoma wasscanned. Naso-orbital-ethmoid com-
plex fractures were present in two of
seven patients (cases 24 and 25); three
of seven had a comminuted fracture
of the ipsilateral orbital apex (cases 11,20, and 25), and another had a contra-
lateral orbital apex fracture (case 24).Three of the seven patients had frac-tures through the floor of the sellaturcica as the fracture traversed the
sphenoid body (cases 20, 23, and 25).
Variants of the LFD Pattern
In three cases, there was an associ-ated AT fracture (cases 11, 20, and 21),
and in one case there was an associ-ated sagittal fracture through the eth-moid sinuses (case 23). One patient(case 32) had an additional contralat-
Figure 3. Composite drawing of the ATfracture pattern (left impact).
a. b. c.Figure 4. Case 9. Axial CT sections (2-mm sections) of AT fracture pattern resulting from a left temporal impact sustained in a fall. (a) CT scanobtained at the level of the orbital roof shows a transverse fracture through both lesser sphenoid wings (black arrowheads) and a fracture ofthe squamous portion of the left temporal bone (white arrowhead). A longitudinal fracture of the petrous portion of the left temporal bone is
also present. (b) CT scan obtained 6 mm caudal to a reveals a transverse fracture across the planum sphenoidale (arrowheads) and the fracture
of the squamous portion of the left temporal bone (arrow). (c) CT scan at the level of the floor of the middle cranial fossa shows fracturesthrough the left sphenotemporal buttress (curved arrow) and the cerebral surface of the right greater sphenoid wing (arrowheads). This image
demonstrates the normal right sphenosquamosal suture (small solid arrows), the left petrooccipital fissure (large solid arrow), the left jugular
foramen (large open arrow), and the left occipitomastoid suture (small open arrow).
a. b. C.
Volume 188 #{149}Number 2 Radioloev #{149}333
PT Pattern
PT fractures usually have a charac-
teristic inverted U shape, with frac-tures extending from one temporal
bone, across the middle cranial fossato the posterior sphenoid body andclivus, then to the opposite middle
cranial fossa and then on to the oppo-site temporal bone (Figs 10-13). The
hallmark of this fracture pattern is thedemonstration of a transverse fracturethrough the posterior sphenoid sinusor clivus. The exact location of thisfracture varies slightly; it occurs mostfrequently at the posterior wall of thesphenoid sinus but sometimes a few
Figure 5. Case 5. Orbital apex fracture asso-
ciated with anterior transverse fracture re-
sulting from a lateral frontal impact sus-
tained in a motor vehicle accident. An axial
CT section (2-mm width) obtained at the
level of the left orbital apex demonstrates a
portion of the posterior left lateral orbital
wall displaced into the orbit, compressingthe lateral rectus muscle and narrowing the
orbital apex (arrowhead). This patient had a
permanent left oculomotor (CN III) palsy.
Fractures of the left sphenotemporal buttress
(arrow) and the squamous portion of the left
temporal bone are components of the AT
fracture pattern. Both medial orbital walls arefractured.
millimeters anterior or posterior tothis location.
The fracture usually results fromlateral impact to the skull and entersthe skull base in the tympanic portionof the temporal bone anterior to theexternal auditory canal and infero-posterior to the mandibular fossa ofthe temporal bone. Typically, the frac-ture extends into the petrous portionof the temporal bone as either a longi-
tudinal or mixed fracture, which wasseen in ten of 16 cases (cases 14, 15,
27-32, 34, and 35). In four cases, thefracture did not involve the petroustemporal bone (cases 16, 22, 36, and37) and in another case (case 33), the
fracture began as a longitudinal frac-
ture of the petrous portion of the tem-poral bone, bypassing the tympanicportion. In one patient (case 13), thefracture entered the skull further an-teriorly in the squamous portion.
In all but case 13, the fracture thentracks anteromedially along the teg-
men tympani toward the petrousapex. It enters the sphenopetrosalsynchondrosis, which may be dia-
static or show comminution along the
posterior margin of the greater sphe-noid wing. The fracture typically
passes through the foramen lacerum,posterior to the foramen ovale, thencrosses the horizontal portion of thecarotid canal and enters the sphenoid
body. After it traverses the body, thefracture line enters the contralateralsphenopetrosal synchondrosis, mir-roring the opposite side. It continuesto the petrous apex and then usuallyexits the skull base through the tym-panic and squamous portions of thetemporal bone near the zygomaticprocess. This site of exit was observed
in 10 of 16 patients (cases 13, 15, 16,28-30, 33, and 35-37). In five addi-
tional patients (cases 14, 27, 31, 32,and 34), the fracture extended intothe petrous portion, with the fractureexiting the skull base through themastoid. In one patient (case 22), theexiting fracture showed a variation,which will be discussed below. Ingeneral, the PT fracture is symmetricfrom side to side, with an invertedU-shaped cleft formed through the
posterior middle cranial fossa.
Variants of the PT Pattern
In a few cases, we observed varia-tions from the typical PT pattern. In
one patient (case 13), the fracture en-tered the skull base more anteriorly,across the squamous portion of the
temporal bone at the base of the zy-goma, anterior to the mandibularfossa. It then extended across the pos-
tenor aspect of the greater wing ofthe sphenoid bone, anterior to thesphenopetrosal synchondrosis. Onceacross the sphenoid body, the fracture
followed the typical course throughthe contralateral sphenopetrosal syn-chondrosis. In four other patients
(cases 14, 30, 33, and 36), both the
more typical entry site and this van-ant entry site coexisted.
Another subset of the PT fracture
pattern displayed variation in thefracture exit site. In one (case 22), theexiting fracture swung far anteriorlyafter leaving the sphenoid body,crossing the sphenoidal plane andterminating in the contralateral or-bital roof. In another (case 27), in ad-dition to the typical exit fracturealong the temporal bone, one fractureextended through the cerebral surfaceof the greater wing of the sphenoidand another ran along the occipitalbone. This occipital fracture entered
Figure 6. Case 12. Axial CT scans (3-mm sections) show AT fracture pattern with an oblique component, resulting from a right frontoparietalimpact caused by a large blunt missile. (a) CT scan obtained at the level of the right orbital roof demonstrates a diastatic fracture of the right
lateral orbital wall (arrowhead). A fracture of the squamous portion of the right temporal bone is also present. (b) CT scan obtained at the levelof the sphenoidal plane shows the oblique fracture extending from the right medial orbital wall to the base of the left anterior clinoid process
(arrowheads). (c) CT scan obtained at the level of the floor of the left middle cranial fossa reveals the oblique fracture terminating in the cere-
bral surface of the left greater sphenoid wing (arrowhead).
334 #{149}Radiology August 1993
Figure 7. Composite drawing of the LFD
pattern (left impact). The dotted line indi-
cates the less common pathway.
a.
Figure 9. Case 20. LFD pattern fracture re-sulting from a left lateral frontal impact sus-tained in a motor vehicle accident. Axial CTscan (2-mm section width) at the level of the
maxillary sinuses shows a fracture through
the anterior and posterolateral walls of the
left maxillary sinus and the inferiorly dis-
placed left orbital floor (solid arrows). Thefracture continues in the same plane to in-volve the left lateral wall of the sphenoid si-
nus (arrowheads) before turning to the trans-verse plane at the posterior wall of the
sphenoid sinus (open arrow). An AT fracturewas seen at higher levels (not shown).
the petrooccipital fissure and ex-tended through the jugular foramenand then along the occipitomastoid
suture. Another patient (case 32) had
a similar contralateral occipital frac-ture in addition to the typical contra-
lateral temporal bone fracture. Fourother patients had bilateral occipital
fractures in association with the PT
fracture pattern. In two of the four(cases 34 and 35), the fractures
tracked along the lateral margins of
the occipital bones in bilateral symme-try. In the two others (cases 36 and
37), the fractures traversed the floor ofthe occipital bone across the foramenmagnum. Five patients (cases 13-16
and 22) had an associated AT pattern.
MD Pattern
Three patients (cases 38-40) inwhom the impact was mastoid had
diagonal fractures extending from theipsilateral occipital bone at the occipi-
tomastoid suture across the jugular
foramen to the petrooccipital fissureand into the sphenoid body (Figs 14-
16). The fractures crossed the sphe-noid sinus diagonally and exited itanteriorly across the sphenoidalplane. In two cases, the fractures ter-minated in the contralateral ethmoidair cells (cases 38 and 40), and in one(case 39), the fracture terminated inthe contralateral orbital roof. In allcases, there were ipsilateral temporalbone fractures with associated diasta-sis of the ipsilateral sphenopetrosalsynchondrosis. The MD pattern andsome PT fractures are similar, with
b.
Figure 8. Case 23. Axial CT scans (2-mmsections) show LFD fracture pattern resulting
from a left lateral frontal and zygoma impact
sustained in a motorcycle accident. (a) The
left lateral orbital wall has a comminuted
fracture at the impact site (arrow). Several
nondisplaced fractures in the posterior eth-
moid air cells extending into the sella are
components of the associated anterior sagit-
tal fracture (arrowheads). (b) CT scan ob-
tamed at the level of the floor of the middle
cranial fossa shows a continuation of the
fracture in the inferior portion of the left lat-
eral orbital wall (curved arrow). The fracture
continues into the anterior wall of the sphe-
noid sinus (straight solid arrow). The poste-
nor extent of the fracture is seen in the
mildly diastatic sphenopetrosal synchondro-
sis (arrowheads), and the fracture exits the
skull base in the tympanic portion of the
right temporal bone (straight open arrow).
fractures bordering either side of the
ipsilateral petrous bone, but two key
elements separate these patterns. The
MD fracture crosses the sphenoidbody diagonally from posterior to an-
tenor, whereas the PT fracture crosses
transversely. Also, the MD fracture
terminates in the contralateral ante-
rior cranial fossa, whereas the PT frac-ture typically terminates in the con-tralateral temporal bone.
Patient Outcome
Twenty-nine of the 40 patients sur-vived to be discharged from the hos-pital. Detailed information regardingcomplications was available from themedical records of most of these pa-tients, but in some cases, information
Figure 10. Composite drawing of the PT
pattern (left impact). The two solid lines on
the side of impact indicate that the fracture
typically involves both the tympanic and pe-
trous portions of the temporal bone. The dot-
ted line on the opposite side illustrates the
less common pathway for the exiting fracture.
regarding a particular complication
was not recorded. Cognitive deficit
was common among the 25 survivingpatients in whom the cognitive statusat the time of hospital discharge wasrecorded. Twenty (80%) of these 25patients were cognitively impaired,and five (20%) were considered nor-mal.
Cranial nerve (CN) injuries wererecorded in 16 (57%) of the 28 surviv-
Figure 14. Composite drawing of the MDpattern (left impact). The dotted line illus-
trates an alternate pathway for the exiting
fracture.
Figures 11, 12. (11) Case 16. Axial CT scan (10-mm section width) shows PT pattern fractureresulting from a left temporal impact sustained in a motorcycle accident. This CT section was
obtained at the level of the floor of the middle cranial fossa and shows most of the course of
this fracture. The fracture enters the skull base in the tympanic portion of the left temporal
bone, not involving the left petrous portion. It continues into the left sphenopetrosal syn-
chondrosis, crosses the clivus transversely, and then extends into right sphenopetrosal syn-
chondrosis (arrowheads). The exit in the tympanic portion of the left temporal bone is not
shown on this scan. (12) Case 33. PT pattern fracture resulting from a left temporal impact sus-
tamed when the patient was struck by a motor vehicle. Axial CT scan (10-mm section width)obtained at the level of the floor of the middle cranial fossa demonstrates the entire course ofthe fracture, beginning in the left petrous portion of the temporal bone, continuing mediallyinto the left sphenopetrosal synchondrosis, crossing the clivus in the transverse plane, enter-
ing the right sphenopetrosal synchondrosis, and terminating in the tympanic portion of the
right temporal bone (arrowheads). The absence of a fracture in the left tympanic portion is an
unusual feature in this case.
a. b.Figure 13. Case 31. Axial CT scans (1.5-mm section width) show PT pattern fracture resultingfrom a right mastoid impact sustained in a motor vehicle accident. (a) Scan obtained at thelevel of the external auditory canal reveals the fracture extending from the tympanic portion
of the right temporal bone into the sphenopetrosal synchondrosis (arrowheads), immediatelyanterior to the carotid canal. Fractures of the posterior aspects of both lateral sphenoid sinuswalls indicate the course of the fracture across the sphenoid body in the posterior coronal
plane (solid arrows). The inferior margin of a fracture that extends from the mastoid processinto the petrous portion of the right temporal is noted (open arrow). (b) CT scan obtained 6mm cephalad to a at the level of the floor of the sella turcica shows the transverse fracturecrossing the roof of the sphenoid sinus in the posterior coronal plane (arrowheads). A mixed
fracture of the right petrous bone is well seen. Fluid in the left mastoid antrum is a sign of the
longitudinal fracture of the petrous bone seen at higher levels.
ing patients for whom records wereavailable. Peripheral facial nervepalsy (CN VII) was the most frequent,
11. 12.
Volume 188 #{149}Number 2 Radiology #{149}335
occurring in eight patients (29%).These patients had either LFD or PT
fractures involving the temporal bone
near the course of the facial nerve.
One of the eight had a small, focalhemorrhage in the midline anterior
midbrain; none had CT evidence ofpontine hemorrhage. Traumaticblindness (CN II) was present in
seven patients (25%), all of whom had
AT fracture patterns, which by defini-
tion involve the orbital apex. Sevenpatients with the AT pattern showedevidence of comminution at the or-bital apex, but only four of these pa-tients had traumatic blindness. Paral-
ysis of extraocular motion was also acommon complication, with oculomo-ton nerve (CN III) palsy occurring inseven (25%) of the surviving patients.
Five of these patients had AT frac-tunes, one had an LFD fracture, andanother had a PT fracture. Trochlearnerve (CN IV) palsy occurred in onepatient (4%) who had a PT fracture,and abducens (CN VI) palsy occurred
in three patients (11%) who had ei-ther a PT or LFD fracture. All patientswith trochlear and abducens palsyhad an associated facial nerve (CNVII) palsy. Two patients (7%), both ofwhom had PT fractures, had trigemi-nal (CN V) nerve dysfunction. Bothalso had associated facial nerve (CNVII) palsy.
Seven (25%) of the 28 survivingpatients for whom records were avail-able had cerebrospinal fluid (CSF)leaks. CSF rhinorrhea occurred inthree patients, all of whom had ATfractures. CSF otorrhea occurred in
one or both ears in six patients whohad fractures involving the temporal
a. b.
Figure 15. Case 39. Axial CT scans (10-mm section width) depict MD pattern fracture result-ing from a right temporomastoid impact sustained in a motor vehicle accident. (a) CT scan
obtained at the level of the floor of the posterior cranial fossa demonstrates a comminutedfracture of the right mastoid process and right occipital bone on either side of the occipitomas-toid suture (arrowheads). (b) CT scan obtained 10 mm cephalad to a shows diastasis of the
right petrooccipital fissure (arrow). The fracture then follows a diagonal course through the
sphenoid body (arrowheads). This fracture terminates in the left orbital roof (not shown). An
associated fracture of the right petrous portion of the temporal bone and diastasis of the rightsphenopetrosal synchondrosis is noted (open arrows).
336 #{149}Radiology August 1993
bone. CSF leaks were also observed infour (36%) of the 11 patients whodied. Diabetes insipidus was noted inone surviving patient (4%) and oc-curred prior to death in three otherpatients. Vascular complications wereuncommon; carotid-cavernous fistulasdeveloped in two patients.
Hearing loss occurred in 10 (38%)of the 28 surviving patients. Detailsregarding the type of hearing losswere available in six of these patients.Four had conductive loss, one hadsensorineunal loss, and one had amixed hearing loss. Temporal bonefractures on the side of hearing loss
were present in all cases.Of the 40 patients with transsphe-
noid basilar skull fractures, 11 (28%)died as the result of their head inju-ries. The likelihood of death varied
with the fracture pattern. One (9%)of the 11 patients with a pure ATfracture died. One (33%) of threepatients with the anterior sagittalT-shaped fracture associated with theAT pattern died. Three (19%) of 16patients with PT fractures (one ofwhom also had an AT fracture) died.Four (57%) of seven patients with theLFD pattern died. Three of these pa-tients also had associated AT fnac-tunes, and the other had an associated
anterior sagittal fracture. Two (67%)of three patients with the MD patterndied. Overall, six of 10 patients (60%)with diagonal fractures and five of 30(17%) with an exclusively transverse
pattern died. Mortality for patientswith a diagonal skull base fracturepattern was significantly higher thanthose who had only a transverse frac-
tune pattern (Fisher exact test; P =
0.014).Review of the CT scans obtained in
patients who died revealed that thepresence of one or more of the follow-ing features was associated with earlymortality: severely comminuted frac-tune at the impact site, widely dia-static fractures, or a diagonal fracturecourse across the sphenoid body. One
or more of these features were pres-ent in all of the six patients who diedin the first 2 days after admission.They were present in one patientwho died on day 7 and in one patientwho survived in a persistent vegeta-tive state. By inference, these featuresmay serve as indicators of more se-
vere cenebral injury.
DISCUSSION
This examination of 40 patientsdemonstrates that transsphenoid basi-lar skull fractures fall into a few dis-crete patterns of fractures traveling
along well-defined lines of weakness.In this study, patients had fracturesextending in a coronal plane throughthe sphenoid bone. In AT fractures,this plane runs through or adjacent to
the anterior wall of the sphenoid si-nus. In PT and LFD fractures, the con-onal fracture nuns through on imme-diately adjacent to the posterior wallof the sphenoid sinus. The location ofthese fractures through the sphenoid
body is not surprising, because the
anterior and posterior walls of thesphenoid sinus are points of transi-tion. Anteriorly, this transition is fromthe honeycomb of well-reinforcedethmoid air cells to the relatively un-supported lateral walls of the sphe-noid sinus. Posteriorly, the transitionis from the solid cancellous bone of
the clivus to the thin plates of corticalbone that compose the lateral walls ofthe sphenoid sinus. Thus, forcestransmitted along the strong spheno-temporal buttress anteriorly and thepetrous portions of the temporal boneposteriorly fracture along these coro-nal planes of weakness as they crossthe sphenoid body.
Another reproducible line of weak-ness is the sphenopetrosal synchon-
drosis. This fibrocartilaginous band,
forming the junction between thegreater sphenoid wing and the pe-trous portion of the temporal bone, is
the common pathway for all but theAT fractures as they pass to or fromthe sphenoid body. It is surroundedby the carotid canal posteriorly andthe foramen ovale anteriorly, bothpotential weak points. These struc-
Figure 16. Case 40. Axial CT scan (2-mmsection width) obtained at the level of theexternal auditory canal depicts MD patternfracture resulting from a right mastoid and
parietooccipital impact sustained in a motor
vehicle accident. Marked diastasis of the
petrooccipital fissure (arrowhead) is evident.
The fracture extends into the posterior aspectof the sphenoid sinus on the right and pur-sues a diagonal course through the sphenoidbody (arrows).
tunes are sometimes fractured, but it isthe synchondrosis itself that is almostuniformly involved.
The patterns of fracture describedherein correspond closely to the pat-terns described on the basis of au-topsy data in the early part of thiscentury by Rawling (16). Specifically,the PT fracture is his “typical basic
fracture.” Our finding that most frac-tures enter the skull base anterior tothe auditory canal, extend through
Vnliime 1�R #{149}Number 2 Radinln�v #{149}�7
the sphenopetrosal synchondrosis,cross the posterior sphenoid body,
and then pass through the corre-sponding structures on the oppositeside matches Rawling’s descriptionprecisely. The variant pathway pass-
ing diagonally to the anterior cranialfossa on the contralateral side seen in
case 22 of our study is also includedin Rawling’s original description.
The LFD pattern corresponds to asimilar pattern described by Rawling.We have found that impact force istransmitted along the lateral walls ofthe maxillary sinus and orbit, whileRawling placed emphasis on the visi-ble fracture of the orbital roof. Fur-then, most of our patients had frac-tunes that crossed the posterior
sphenoid body in the coronal plane,whereas Rawling’s illustration mdi-cates a diagonal pathway. Still, thefractures are essentially equivalent. Itis the detail available from thin-sec-
tion CT that allows us to make thesefine distinctions that would not beevident at autopsy. The MD patterncorresponds to an identical fracture in
Rawling’s work. All of our cases alsohave an ipsilateral temporal bonefracture extending to the sphenope-trosal synchondrosis, which was notpart of the original description byRawling. Thus, three of the four ma-jon fracture patterns that we haveidentified on the basis of CT findingsin living patients are essentially thesame as the patterns defined 80 yearsago on the basis of autopsy studies.
The AT fracture pattern, which isthe most common fracture in our se-ries, was not described by Rawling.Five similar cases, however, were in-cluded by LeCount and Hockzema intheir review of 80 symmetrical trau-matic fractures of the cranium (17).
None of the fractures presentedherein are new, but review of the ra-diologic literature reveals that these
fracture patterns have not been recog-nized in imaging studies, even withthe widespread use of CT in patientswith head injuries (2,4,5,10,12,18,19).Several articles have included illustra-tions of AT and PT fractures, but theterminology established three genera-tions ago by neurosurgeons and pa-thologists has not been used in imag-
ing studies (8,11,20). Thus, part of the
value of our work is in the reintroduc-
tion of the systematic analysis of basi-
lar skull fractures and the application
of this system to CT scanning in living
patients.
Implicit in our work and in previ-ous studies is the concept that the siteof impact is a major factor in deter-mining the fracture pattern. We have
found this generally to be true. LFDfractures occurred only after lateralfrontal or zygoma impacts. MD frac-tures occurred with impacts to themastoid and adjacent portions of thetemporal bone. Anterior sagittal frac-tures occurred with medial frontalimpacts. AT fractures occurred withvarious anterior skull impacts rangingfrom the medial frontal region to thetemporal region. The PT fractures alsooccurred with a broader range of im-pact sites, ranging from the temporalto the occipital region.
In several cases, however, morethan one fracture pattern was pres-ent, presumably induced by a singleimpact. Also, we encountered oneexception to the general correspon-dence between impact site and frac-tune pattern. In case 4, a mastoid im-pact resulted in an AT fracture, notthe expected PT fracture. In their au-topsy study of “typical” basal skull
fractures (PT fractures), Harvey andJones showed that this pattern canarise from posterior, lateral, and fron-
tal impacts (21). They concluded thatthe PT fracture pattern is not a reli-able indicator of impact site. On thebasis of all of this information, we
conclude that there is a general rela-tionship between impact site and re-sulting fracture pattern. There is vari-ability both in the fracture patterns
produced by an impact at a given siteand in the sites of impact responsiblefor a given fracture pattern. The latteris particularly true in the case of the
PT fracture.Fracture pattern recognition has
value in prediction of patient out-come and likely complications. First,patient mortality was significantlymore likely among patients with diag-onal fracture patterns than withtransverse fractures. Most fatal inju-ries occurred from high-speed motorvehicle accidents producing markedlycomminuted fractures at the impactsite, widely diastatic fractures, and/or
diagonal fractures across the sphe-noid body. We suggest that less se-vere impacts will produce fracturesalong the well-established lines ofweakness causing either the AT or PTfracture pattern predominantly, whilediagonal fracture patterns, often ac-
companied by severe impact site com-minution and fracture diastasis, re-quire higher energy deposition andthus lead to more severe cerebral in-jury.
The second area where the fracturepattern has predictive value is cranialnerve deficits and other complicationsarising from injuries to soft-tissue struc-tures in proximity to the fractures. The
AT pattern is associated with traumaticblindness (CN II), oculomotor nervepalsy (CN III), and CSF rhinorrhea.
The LFD pattern is associated withipsilateral oculomotor (CN III), con-tralateral abducens (CN VI), and facial(CN VII) palsy and with contralateral
hearing loss. The PT pattern is associ-ated with trochlear (CN IV), trigemi-nal (CN V), abducens (CN VI), andfacial (CN VII) palsies and with hear-ing loss. Temporal bone fracture, re-gardless of associated fracture, is thebest indicator of CSF otorrhea. Tem-poral bone fractures occurred in allpatients with LFD and PT fracturesbut also occurred as a separate frac-ture in a few patients with AT frac-tunes. Insufficient numbers of surviv-ing patients with the MD patternprecludes analysis of complicationsassociated with this pattern. Diabetesinsipidus and vascular complicationsoccurred too infrequently to makegeneralizations about associated frac-ture patterns. Cognitive deficits wereso common that there was no appar-
ent difference in their prevalenceamong the various fracture patterns.
There are some limitations attrib-uted to the retrospective nature ofour study. First, because we were mi-
tially interested in basilar skull frac-ture resulting from lateral impacts,patients with midline frontal impactwere excluded from the study. Thus,sagittal fractures extending from thefrontal sinus through the ethmoidbone to the sphenoid body and con-tinuing into the posterior cranialfossa, which were described by Rawl-
ing, were not included in the study.
Similarly, fractures resulting from oc-cipital impacts that involve only theposterior cranial fossa and the lateralportions of the middle cranial fossa,sparing the sphenoid body, are alsonot represented in our study. Second,since the recognition of the fracture
pattern is the first step in identifica-tion of cases for retrospective review,we believe that the AT pattern isprobably underrepresented in ourretrospective cases. In fact, it is by farthe most common pattern in the caseswe identified prospectively. There-fore, we have drawn no conclusionswith regard to the relative prevalenceof these fracture patterns. Third, cer-tam details of the fractures were prob-ably not detected in patients whowere studied with older CT scannersand in those who died without hay-ing undergone thin-section studies.This may result in underreporting of
associated fractures. Fourth, sincemedical records were incomplete in afew cases and since many patients
338 #{149}Radiology August 1993
had such profound cognitive deficitsthat detailed neurologic examinationswere not recorded, the incidence ofcomplications resulting from the frac-tures is probably also underestimated.
Still, given these limitations, webelieve that our study is important inthe rediscovery of the early work ofRawling and the application of hismodel to patients studied with CT.We have shown that these fracturepatterns have predictive value withregard to patient mortality and frac-ture complications. More important,we have introduced a systematic ap-proach to the imaging evaluation ofbasilar skull fractures, where previ-ously only parts of the whole wereunderstood. #{149}
References1. Nelson EL, Melton U III, AnnegersJF,
Laws ER, Offord KP. Incidence of skullfractures in Olmsted County, Minnesota.Neurosurgery 1984; 15:318-324.
3. Betz BW, Wiener MD. Air in the temporo-mandibular joint fossa: CT sign of temporalbone fracture. Radiology 1991; 180:463-466.
4. Dolan KD, Jacoby CG. Radiology of basi-
lar skull fractures. CRC Crit Rev Diagn Im-aging 1979; 12:101-152.
5. Ghobrial W, Amstutz S, Mathog RH. Frac-hires of the sphenoid bone. Head NeckSurg 1986; 8:447-455.
6. Holland BA, Brant-Zawadzki M. High-resolution CT of temporal bone trauma.AJR 1984; 143:391-395.
7. Jend HH, Jend-Rossman I. Sphenotempo-ral buttress fracture: a report of five cases.Neuroradiology 1984; 26:411-413.
8. Joslyn JN, Mirvis SE, Markowitz B. Com-plex fractures of the clivus: diagnosis withCT and clinical outcome in 11 patients. Ra-diology 1988; 166:817-821.
9. Johnson DW, Hasso AN, Stewart CE III,Thompson JR. 1-linshaw DB Jr. Temporalbone trauma: high-resolution computedtomography evaluation. Radiology 1984;151:411-415.
10. Keeling FP, Ayers AB, Field S, Forbes W, etal. Fracture of the sella turcica: a report ofthree cases. Clin Radiol 1986; 37:233-234.
12. Sanders BB, VanderArk GD. Transversefractures of the clivus. J Neurosurg 1973;39:610-614.
13. Unger JM. Orbital apex fractures: the
contribution of computed tomography.Radiology 1984; 150:713-717.
14. Braun IF, Nadel U. The central skull base.In: Som PM, Bergeron RT, eds. Head andneck imaging. 2nd ed. St Louis, Mo: Mos-by-Year Book, 1991; 875-924.
15. Williams PL, Warwick R, Dyson M, Bannis-ter UH. Anatomy of the human body.37th ed. New York, NY: Churchill Living-stone, 1980; 360-365,373-381.
16. Rawling LB. Fractures of the skull. In:The surgery of the skull and brain. Lon-don, England: Oxford University Press,1912; 68-134.
17. LeCount ER, Hockzema J. Symmetricaltraumatic fractures of the cranium: symmet-ricalfragmentation-comments on their
![Basilar Membrane Responses to Two-Tone and Broadband Stimuli [and Discussion]](https://static.documents.pub/doc/80x56/635166dd8624f8c9710ef8db/basilar-membrane-responses-to-two-tone-and-broadband-stimuli-and-discussion.jpg)
