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Louis M. Teresi, MD #{149}Robert B. Lufkin, MD #{149}Fernando Vinuela, MDS Rosiland B. Dietrich, MD #{149}Gabriel H. Wilson, MD
#{149}John R. Bentson, MD #{149}William N. Hanafee, MD
MR Imaging of the Nasopharynx andFloor of the Middle Cranial Fossa
Part I. Normal Anatomy’
811
Head and Neck Radiology
The normal anatomy of the naso-pharynx and floor of the middle cra-nial fossa was analyzed with mag-netic resonance (MR) imaging. MRimages from five healthy volunteerswere correlated with whole-organcryomicrotome sections from threecadavers. Anatomic connections ex-ist between the paranasopharyngealspaces and the surface structures ofthe skull base. These anatomic con-nections include the intimate rela-tionship between the eustachiantube and the pharyngobasilar fascia,the attachment of the muscles ofmastication and deglutition to theskull base, and vascular and nervousstructures in the foramina. The in-herent contrast between the soft tis-sues of the nasopharynx and relatedstructures and the bone of the floorof the middle cranial fossa allowedexcellent visualization of these ana-tomic connections.
Index terms: Head, MR studies, 10.1214 #{149}Naso-
pharynx, anatomy, 263.92 #{149}Nasopharynx, MR
studies, 263.1214 #{149}Skull, anatomy, 10.92
Radiology 1987; 164:811-816
1 From the Department of Radiological Sci-ences, University of California Los AngelesSchool of Medicine, Los Angeles (L.M.T.,R.B.L., F.V., R.B.D., G.H.W., J.R.B., W.N.H.).From the 1986 RSNA annual meeting. Received
November 18, 1986; revision requested Febru-ary 10, 1987; revision received April 14; accept-
ed May 6. Supported by Public Health Servicegrant number 1K08 CA 00979-01, awarded bythe National Cancer Institute, Department of
Health and Human Services. Address reprintrequests to L.M.T., Department of Radiology,UCLA Medical Center, BL-428, Los Angeles,CA 90024.
c RSNA, 1987See also the articles by Teresi (pp. 817-821)
and Som (pp. 825-832) in this issue.
W HENEVER a new imaging tech-
nique is applied to a region of
the body it is imperative to first de-
termine what anatomic structures can
be consistently visualized and what
their normal appearance is. The val-
ue of magnetic resonance (MR) in the
evaluation of parts of the skull base
has been described (i-4). The floor of
the middle cranial fossa is frequently
involved in pathologic conditions of
the nasopharynx and related spaces;
the anatomy is complex. This study
was undertaken to delineate the nor-
mal anatomy of the nasopharynx and
floor of the middle cranial fossa as
seen on MR images by correlating
MR images of healthy volunteers
with whole-organ cryomicrotome
sections from cadavers. Special atten-
tion was given to anatomic structures
connecting the nasopharynx and me-
lated spaces with the middle cranial
fossa.
MATERIALS AND METHODS
MR images from five healthy volun-teers were compared with matchedwhole-organ sections obtained from threecadavers. MR examinations of the naso-
pharynges of healthy volunteers were
performed with a 0.3-T permanent-mag-
net imaging system (Fonar B-3000; Fonar,
Melville, N.Y.) with the use of either a so-lenoid surface or a 24-cm bore head re-
ceiver coil. Images were acquired using amultisection two-dimensional Fourier
transform rapid spin-echo (SE) technique
with a repetition time (TR) of 500 msecand an echo time (TE) of 28 msec (SE 500/28). Four excitations in a 256 X 256 matrix
for each image usually were used with asection thickness of 5 mm and 7-mm sep-arations from center-to-center section.Other images were similarly acquiredwith 384 phase-encoding levels and inter-polated to a 512 X 512 display matrix
which decreased the pixel size from 0.75x 0.75 mm to 0.5 X 0.5 mm. Seven simul-
taneous sections were obtained in eachsequence with a total imaging time of 8.5mm (256 X 256 matrix) or 12.8 mm (512 X
512 matrix). Images were obtained in
axial, coronal, and sagittal planes.Whole-organ sections from the cadav-
ers were prepared using a cryomicrotomefreezing and sectioning technique de-scribed by Rauschning et al. (5). The spec-imens were first prepared with an injec-
tion of a pigmented barium compound topermit identification of arteries andveins. In order to preserve topographic
anatomy, the soft tissues to be examinedwere frozen in situ in respect to theirskeletal structures before there had beendraining of blood or other fluids from theregion of interest. The frozen specimenswere transferred to a horizontal section-ing, heavy-duty sledge cryomicrotome
(LKB 2250; Broma Co.; Stockholm, Swe-den). Inside the freezing compartment of
the cryomicrotome, the specimens weremounted on a bed that weighed approxi-
mately 400 pounds (181.8 kg). This heavyweight prevented vibrations and insuredan even shaving slice. The microtomeknife sectioned the specimens at prede-termined thicknesses varying from 5-50
Mm. When photography was desired, thesurface of the specimen was gentlyrubbed with a warm cloth soaked in eth-ylene glycol to produce a frost-free sur-
face. Photographs of representative grosssections were then compared with the re-
spective MR images from the healthy vol-unteers.
RESULTS
MR Images of Normal Anatomy
The nasopharynx is an inverted J-shaped muscular sling suspended
from the floor of the middle cranial
fossa. Involved in both deglutition
and respiration, the nasopharynx
connects with the nasal cavity anteni-
only and with the omopharyngeal cay-
ity infeniorly. It is bounded superior-
ly by the floor of the sphenoid bone
and the clivus, posteriorly by the pre-
vertebral musculature of C-i and C-2,
and laterally by the pamapharyngeal
constrictor muscles and deep soft tis-
sues of the panapharyngeal space and
infratemporal fossa.
Superficial soft tissues-At upper
levels of the nasopharynx, the bilat-
b. c.
e.
Figure 1. Serial axial (SE 500/28) MR images and matched whole-organ cryosections from lowest level (a) to highest level (c). (a) Level of
the eustachian tube orifice. (b) and (d) Level of the high nasopharynx. (c) and (e) Level of the sphenopalatine foramen and pterygoid canal.
Refer to key for definitions of abbreviations.
Key for Figures
C clivus Iji levator palatini muscle Pf pterygopalatine fossa
Ca carotid artery lpp lateral pterygoid plate PG parotid gland
CC carotid canal it lymphoid tissue �n’ pterygoid veins
cFL cartilaginous base of foramen lacerum M maxillary sinus pvc pterygo-vaginal canal
Cs cavernous sinus Ma mandible RC rectus capitus muscle
fT eustachian tube i�za maxillary artery branches S sphenoid sinus
t’fO eustachian tube orifice MC Meckel cavity Sf sphenopalatine foramen
FL foramen lacerum ME middle ear Srnf sphenomaxillary fissure
FO foramen ovale Mf middle cranial fossa SOf superior orbital fissure
FR foramen rotundum ninia middle meningeal artery SP soft palate
fR fossa of Rosenmueller MP medial pterygoid muscle ST sulcus tubae auditivae
fS foramen spinosum nip medial ptervgoid plate T temporalis muscle
GW greater wing of sphenoid Ms masseter muscle TG trigeminal ganglion
HP hard palate on orbital apex tp tensor palatini muscle
lot inferior orbital fissure �,l optic nerve TT torus tubarius
IT inferior turbinate P pterygoid process V trigeminal nerve
JF jugular foramen �a palatine artery Vi ophthalmic nerve
Iv jugular vein PA petrous apex V2 maxillary nerve
LC longus coli muscle phf pharyngobasilar fascia V.3 mandibular nerve
LP lateral pterygoid muscle Pc ptervgoid canal
812 #{149}Radiology September 1987
b. c.
Volume 164 Number 3 Radiology #{149}813
e.
g.
Figure 2. Serial coronal (SE 500/28) MR images and matched whole-organ cryosections from most anterior level (a) to more posterior level
(g). (a) and (b) Level of the sphenopalatine foramen. (c) Level of pterygopalatine fossa and anterior pterygoid process. (d) and (e) Level of
foramen ovale. (f) and (g) Level of foramen lacerum. Refer to key for definitions of abbreviations.
enally paired recesses of the airway
are a characteristic finding (Figs. la,
2c). The orifice of the eustachian tube
is seen just anterior (on axial images)
or inferior (on coronal images) to the
torus tubanius, the most prominent of
the superficial landmarks of the na-
sopharynx. The cartilaginous end of
the eustachian tube is usually of simi-
lam or lower signal intensity than sum-
rounding muscles. If tubular tonsillan
tissue is present, this area may have a
fairly intense signal depending on
the amount of lymphoid tissue pres-
ent and the effects of volume averag-
ing. The lateral pharyngeal recess
(fossa of Rosenmueller) is an air-
filled space which projects posterior
to the torus tubamius and muscular
prominence of the levaton palatini
muscle.
Lymphoid tissue lines the muscu-
lam sling of the nasopharynx and is
most prominent along the roof of the
nasopharynx. The signal of lymphoid
tissue is always more intense than
that of muscle (Fig. la, ib). This
bright strip of lymphoid tissue lines
the roof and walls of the nasophar-
ynx, often filling the fossae of Rosen-
814 #{149}Radiology September 1987
mueller. On axial images of the lowerairway, hypentrophied lymphoid tis-sue may have a lobulated on undulat-ing surface contour. On coronal im-ages it will appear to hang down
from the roof of the nasopharynx(Fig. 2c). The lymphoid tissue of thepharyngeal tonsil (adenoids) is nor-
mally located submucosally and willnever obliterate the deeper tissueplanes surrounding the nasopharynx.
Deep to the lymphoid tissue arethe palatal and phanyngeal muscles(6) (Figs. la, 2d, 2e, 2f). The levator
veli palatini muscle, some of whosefibers anise from the short limb of thecartilaginous eustachian tube, onigi-nates from the quadmate area of thepetrous bone. The tensor ve!i palatinimuscle originates from the scaphoidfossa of the sphenoid bone antemola-teral to the levatom veli palatini mus-cle. The levator veli palatini muscleand the cartilaginous portion of theeustachian tube pass directly to thesoft palate through an aperture in thepharyngobasilar fascia called the si-
nus of Mongagni (6). The tensor veli
palatini muscle reaches the palate in-directly by hooking around the ham-ulus of the medial pterygoid plate.These muscles are routinely visible asbands of intermediate signal intensi-
ty flanking the airway. At the level
of the hand palate, the superior con-stnictor muscle and Passavant muscle
mainly bound the nasopharynx pos-
terolaterally. On axial images, these
muscles appear as a band of intenme-
diate intensity surrounding the later-
al and posterior walls of the airway.Other muscles that contribute to thesignal intensity in this region in-dude the tensor veli palatini, levatorveli palatini, salpingopharyngeus,and palatopharyngeus.
Parapharyngeal space and infratem-
poral fossa.-The panapharyngeal
space lies latenial to the palatal mus-des and extends from the base of theskull to the oropharynx (Figs. la, lb.2d, 2f, 3a). Its boundaries are definedby the buccopharyngeal fascia. The
medial part of the buccopharyngealfascia is the epimysium of the supeni-or phanyngeal constrictor muscle.
The lateral boundary of the bucco-pharyngeal fascia is a reflection of
the deep cervical fascia, which coversthe deep surface of the panotid glandand pterygoid muscles. These layersare sparse and loosely applied totheir respective muscles of origin toaccommodate the tremendous move-ment of the pharynx that occurs dun-ing swallowing. The buccopharyn-geal fascia is not visible on computedtomography scans or MR images, but
it forms the medial and lateralboundaries of the parapharyngealspace. The paraphanyngeal space ap-
pears as a loose network of high-sig-na! fibrofatty tissue and is alwayssymmetric. Within the parapharyn-
geal space small branches of the ex-ternal carotid artery, pharyngealveins, and mandibular nerve are seenas round or linear, medium- to low-intensity structures.
The infratemponal fossa lies lateralto the paranasopharyngea! space. It isbounded anteriorly by the posteriorwall of the maxillary antrum and lat-enally by the deep head of the tem-poralis muscle and the zygomatic
arch. The medial and lateral ptery-goid muscles fill the bulk of the in-fratemponal fossa. Superiorly, numer-ous foramina perforate the base of
the sphenoid bone. The largest of thefonamina, the fonamen ovale, is nou-tine!y visible as a defect in the cortex
of the sphenoid bone and is appmeci-ated best on coronal images (Fig. 2d).The orifice of the fonamen ovale issurrounded by fat, within which can
be seen the mandibular branch of thetngeminal nerve. Postemolateral tothe fomamen ovale, the foramen spin-osum provides a pathway for the
meningeal artery. Numerous smallerforamina connect small branches ofthe mandibular segment of the max-il!ary artery and pterygoid plexus ofveins and are infrequently seen on
MR images.Pharyngobasilar fascia and eustachian
tube.-The configuration of the naso-pharynx is determined by the very
tough pharyngobasilar fascia whichattaches to the base of the skull fromthe posterior margin of the medialpterygoid plate to the petrous part ofthe temporal bone immediately infront of the carotid fomamina (Figs. 1,3). Its fibers are continuous with that
of the foramen lacerum (7) (Fig. lb.ld). On axial and coronal images, the
pharyngobasi!ar fascia is seen as a
low-intensity line extending fromthe medial ptenygoid plate to the ca-rotid foramen, medial to the tensorpa!atini muscle. From the carotid fo-ramina, the fascia reflects mediallyover the longus coli and rectus capi-tus muscles. The fascia thus forms an
entirely closed and very resistant fi-
brotic chamber that is continuouswith the fibrous tissue occupying theforamen lacerum. The only apertureis the sinus of Morgagni, for the pas-
sage of the eustachian tube and fibersof the levator palatini muscle. Nearthe skull base the fascia is dividedinto a gutter that is responsible for
the strong attachment of the eusta-
chian tubes to the base of the skulldirectly between the fonamen Ia-
cerum medially and foramen ovale
laterally. This relationship is best ap-
pmeciated on axial images (Fig. ic).The foramen lacerum and foramenovale make up a pathway into the
cranium since they are in direct com-munication with the cavernous sinus.
The eustachian tube travels fromthe skull base to the nasopharynx as a
slowly curving, invented S. Because
of its S-shaped course, only small
segments of it are seen on axial on
coronal images. The bony part, over 1cm long, tapers down from the ante-nor wall of the middle ear to its on-
fice, which is known as the isthmus.The cartilaginous portion, over 2 cmlong, joins the bony part at the isth-
mus and fits into a sulcus on the skull
base, the sphenoid sulcus (sulcus tu-bae auditivae) between the greaterwing of the sphenoid bone and theapex of the petrous portion of thetemporal bone (Figs. ic, le, 3a). Thecartilaginous portion first arches
downward and forward across theparapharyngeal space. Before thepharyngeal orifice, it makes anotherslight curve downward and forward.Only the anterior portion of the can-tilage turns infeniorly from thisplane. Here the torus tubanius rests
against and fits into a small depres-
sion on the posterior margin of the
media! pterygoid plate.Pterygopalatine fossa.-The pterygo-
palatine fossa is a medial depression
of the pterygomaxillary fissure whichlies between the pterygoid process
and the maxillary sinus. On axial andsagittal images it appears as a flat
space filled with high-signal fat(Figs. lc, 2a). The sphenopalatine fo-namen is located at the medial mar-gin of the signal-void perpendicularplate of the palatine bone. The ptery-gopalatine fossa connects with thenasal fossa through this aperture.
The pterygopalatine fossa is in freecommunication with the inferior or-bital fissure superiorly and the infra-
temporal fossa laterally. The foramenrotundum, which appears as a line or
ring of negligible signal, lies within
the greater wing of the sphenoidbone anterior to the point where
the medial pterygoid plate joins thebasisphenoid bone (Fig. lc). Fromhere, the second division of the tn-geminal nerve passes through theupper pterygomaxi!lary fossa form-ing the sphenopa!atine ganglion as itcourses toward the inferior orbitalfissure and infraorbita! groove andcanal. These nerves appear as small,round soft-tissue structures inconsis-
poloti
tube
Styloid process
nt jugular v
mt corotido
Longus andrectus capitus mm
Figure 3. (a) Photograph of normal skull base showing bone landmarks and foramina and
the insertion of the pharyngobasilar fascia (broken line). (b) Composite axial diagram of the
nasopharynx. Right half of the diagram is at a level about 1 cm more cephalad than the left
half. The pharyngobasilar fascia (heavy black line) surrounds the airway and encloses the
cartilaginous end of the eustachian tube and levator palatini muscle. The buccopharyngealfascia (dotted lines) outlines the limits of the prestyloid parapharyngeal space. The potentialretropharyngeal space (dashed line) lies between the pharyngobasilar fascia and the prever-
tebral musculature. CC = carotid canal, FL foramen lacerum, FO foramen ovale, fS fo-
ramen spinosum, JF jugular foramen, lpp lateral pterygoid plate, mp medial pterygoid
plate, pbf = pharyngobasilar fascia, Pc pterygoid canal, pvc pterygo-vaginal canal, Sf
sphenopalatine foramen, ST sulcus tubae auditivae.
Volume 164 Number 3 Radiology #{149}815
round low-intensity structures sun-
rounded by high-intensity fat, the in-
dividual branches are rarely seen.Skull base.-The clivus and basisphe-
noid bone make up the posterior wall
and roof of the nasopharynx. Their
cortical margins show no signal andare seen only by virtue of the con-
trast with interfacing higher-signal
soft tissues (Fig. 2). The intimate rela-
tionship of the mucosa, muscles, and
fat lining the clivus and floor of thesphenoid sinus is seen best on con-
onal images. Fatty marrow within the
clivus and sphenoid bone gives a
characteristic high signal. The ptery-goid (vidian) canal can be seen with-
in the basisphenoid bone as a low-signal, rounded (coronal images) on
linear (axial and sagittal images)structure surrounded by high-signal
marrow (Figs. ic, 2c). Sympatheticand parasympathetic nerves that
course with the internal carotid an-
tery are transmitted through thepterygoid canal with the pterygoidartery to the pterygopalatine and na-
sal fossae.The fomamen lacerum forms a gap
between the anterior tip of the pe-tnous apex and the basisphenoid
bone (upper clivus). This gap is in me-ality filled with cartilage, and the ca-
rotid artery does not go through the
cartilage but lies just above the carti-lage as it leaves the carotid canal toenter the posterior cavernous sinus(Fig. 2f). The cartilaginous base of the
foramen lacenum has virtually no sig-
nal, and only a thin strip of fibrofatty
tissue separates it from the signal-
void carotid artery. Above the fora-men lacemum and lateral to the clivus
Cortuloginous .
end of 15 the cavernous sinus.eustochion tube Vascular channels, the carotid an-
tery, and crania! nerves of the cay-ennous sinus can be resolved consis-
tently on MR images (1) (Fig. 2d).
Coronal images show small foci ofhigh signal that correspond to cranial
nerves transmitted through the cay-
emnous sinus. The abducens nerve(VI) passes through the areolan cavityof the cavernous sinus, and the ocu-lomotor nerve (III) and trochlearnerve (IV) are found in its lateralwall. The optic nerve (II) lies medialto the cavernous sinus. The tnigemi-
nal nerve (V) ganglion and its
branches, within Meckel cavity and
the cavernous sinus, are easily seenon good-quality MR images and havean intermediate signal.
tently seen on MR images. Within gives offbranches to the middle cra- CONCLUSIONthe pterygopalatine fossa, the ptery- ma! and infratempomal fossae, orbit,gopalatine segment of the maxillary nose, palate, and pharynx. Although The skull base, nasopharynx, andartery makes a characteristic loop and segments of the artery are seen as related spaces are crossover areas be-
816 #{149}Radiology September 1987
tween the intra- and extracranial
structures of the head and neck.
Their anatomy is detailed and pre-
sents a formidable task in MR imag-
ing (8-12). Herein we have analyzed
the normal MR anatomy of the naso-
pharynx and floor of the middle cra-
nial fossa by correlating MR images
from healthy volunteers with whole-
organ cryomicmotome sections from
cadavers. Anatomic structures con-
necting the nasopharynx and related
spaces with the middle cranial fossa
have been emphasized. The intimate
relationship of the phamyngobasilan
fascia and eustachian tube to the
skull base has been described in de-
tail. The inherent contrast between
the soft tissue of the nasophamynx
and related spaces and the bone of
the floor of the middle cranial fossa
allows excellent visualization of the
numerous fomamina and fissures of
the skull base connecting the intra-
cranial and extracranial compart-
ments. Coronal and axial images are
most useful in making side-to-side
comparisons of relevant struc-
tunes. U
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