Clinical Radiology (2009) 64, 353e361

REVIEW

Incidental findings on MRI of the spine

S. Kamath, N. Jain, N. Goyal, R. Mansour, K. Mukherjee*

Department of Radiology, University Hospital of Wales, Cardiff, UK

Received 16 May 2008; received in revised form 11 September 2008; accepted 16 September 2008

MRI is widely used as the imaging of choice for spinal disorders and may reveal either a clinically insignificant inciden-

tal abnormality or a significant lesion, unrelated to the spine, which may explain the patient’s symptoms. This articleattempts to establish the importance of such findings and describes a sensible approach to the reporting of MRIexaminations of the spine with special attention to the incidental findings commonly encountered. The MRI charac-teristics of such findings are briefly described.ª 2008 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Introduction

Magnetic resonance imaging (MRI) is well estab-lished as the investigation of choice for spinaldisorders.1,2 Its use is increasing, and the responsi-bility to report lies with both specialists, such asmusculoskeletal or neuroradiologists, as well asgeneral radiologists.

Incidental findings during MRI examinations ofthe spine3e6 are well documented. For the purposeof this article, an incidental abnormality is definedas any disease outside the region of clinical inter-est; for the spine this would include anything otherthan disease related to the vertebral column andthe contents of the spinal canal. Picture archivingand communication systems (PACSs) have been in-troduced in many hospitals to improve reportingefficiency. This has resulted in an increase in thenumber of reported incidental findings and fol-low-up examinations.5,6 This observation may bedue to the fact that images included in pre-PACS,hard-copy studies were often cropped to theregion of interest and none or only limited imagesfrom the localizer scout series were included inpre-PACS hard copies for reporting purposes.Therefore, PACS offers potentially more

* Guarantor and correspondent: K. Mukherjee, Department ofRadiology, University Hospital of Wales, Cardiff CF14 4XW, UK.Tel.: þ44 2920 744887; fax: þ44 2920 743029.

E-mailaddress:kausikmukherjee@doctors.org.uk(K.Mukherjee).

0009-9260/$ - see front matter ª 2008 The Royal College of Radiolodoi:10.1016/j.crad.2008.09.010

information, including uncropped images andlocalizer series, which need review and interpreta-tion. MRI images for examination of the spine mayreveal either a clinically insignificant incidentalabnormality, or a significant lesion unrelated tothe spine, which may explain the patient’s symp-toms. These lesions may lie outside the domainof specialization of the reporting radiologist.Therefore, it is vital that the radiologist is ableto judge whether the lesion requires any furtherinvestigation (e.g., solitary pulmonary nodule,soft-tissue sarcoma, etc) or just a mention in thereport without necessarily needing further fol-low-up (e.g., simple renal cysts, small uterinefibroid, etc).

Incidental findings are also well documented inother techniques.7e13 For example, in one study of3488 patients12 undergoing computed tomography(CT) colonography, 40% of the patients had inci-dental findings, 14% had additional investigations,and 0.8% were given immediate treatment.Furthermore, some patients had more than onesignificant incidental finding. In another retrospec-tive analysis14 of lumbar CT examinations of 100consecutive patients (mean age 68 years, range55e85 years) who presented with low-back pain,three abdominal aortic aneurysms greater than4 cm in diameter were detected. This led the au-thors to recommend using a larger field of viewwhen viewing CT lumbar spine in patients olderthan 55 years of age with low-back pain.

gists. Published by Elsevier Ltd. All rights reserved.

354 S. Kamath et al.

Reporting incidental lesions detected on spinalMRI can have a significant impact on patientmanagement. It is worth remembering that theincidental findings may be more significant thanthe disease of the spine itself. Clinical judgementneeds to be exercised in reporting these incidentalfindings and recommending any further investiga-tion. If appropriate emphasis is not placed it mayresult not only in an increase in the workload forthe reporting radiologist and referring clinician,but also unnecessary gamut of investigations forthe patient.6,15 Conversely, pursuing a significant‘‘incidentaloma’’ may lead to timely interven-tion16 and prevent potentially grave consequencesfor the patient and medicolegal implications forthe concerned radiologist.15 Radiology claims ac-counted for approximately 5% of all closed andpaid claims of the Physician Insurers Associationof America between 1985 and 1998.17 In anotherstudy, analysis of 18,860 lawsuits demonstratedthat 47% of the radiology lawsuits related tomissed diagnoses.18 Therefore, it is imperativethat the relevance of such findings is made known.

For the purpose of this review, a detailed reviewof literature was conducted related to incidentalfindings specifically on MRI of the spine using thePubmed, Medline, Ovid, and Cochrane databases,and the general search engine ‘‘Google’’. Althoughseveral articles detailing the protocols for MRI ofthe spine and interpretation of MRI images wererecovered,2,19e23 only a couple of articles focussedon the detection of incidental findings during MRIexaminations of the lumbar spine.5,6 The latterstudies concentrated on the impact of PACS onthe detection of incidental findings in MRI of thespine. A retrospective review of a total of 2500 re-ports of MRI of the lumbar spine reported 202 inci-dental findings among 183 patients.6 The vastmajority of these incidental findings occurred inthe kidneys, liver, uterus, adnexa, and lymph no-des. Four cases of occult malignancies and onecase of occult metastatic disease were detected.Ultrasound was the most commonly recommendedmode of further investigation followed by CT. An-other study reported 25 incidental findings in 300MRI examinations of the lumbar spine during thetime of PACS implementation at the author’sinstitute.5

Incidental abnormalities arise from a wide rangeof organ systems and the diseases encountered maybe extremely diverse. Also, depending on the MRIsystem used, the localizer pulse sequences mayvary and have an effect on the detection of in-cidental findings. Incidental findings are more likelyto be detected during MRI of the lumbar spine ratherthan thoracic or cervical examinations because of

the higher number of organs and vessels in the fieldof view. An exhaustive list of all the incidentalfindings during MRI examinations of the spine is notpossible as one could potentially encounter anydisease entity in practice. However, based on thepresent authors’ experience and published litera-ture, a list was compiled of the most frequentlydemonstrated incidental findings (Table 1).

Reporting protocols

In our department, MRI of the spine is performedon a 1.5 T MRI system (twin speed; GE Medical Sys-tems, Milwaukee, WI, USA) according to the stan-dard protocol for spinal MRI. Each study includesa three-plane localizer series with a T2-weighted,fast gradient-recalled-echo sequence at56e150 ms/1e3 ms (repetition time/echo time)with a 36 cm field of view, 30� flip angle,256� 128 matrix, 10 mm section thickness, and1 mm intersection gap.

Standard imaging for the lumbar and thoracicspine also includes a sagittal T1-weighted spin-echo (440/14), sagittal T2-weighted fast spin-echo(3500/110), T1 axial (720/14) and T2 axial (4000/103) sequences. In the sagittal sequences, a 36 cmfield of view, 4 mm section thickness, and 1 mm in-tersection gap are used. In axial sequences,a 22 cm field of view, 4 mm section thickness,and 1 mm intersection gap are used. For imagingof the cervical spine the standard sequencesinclude T2-weighted sagittal (3420/114), T1-weighted sagittal (520/9), and MERGE (MultipleEcho Recombined gradient echo) axial. The fieldof view for sagittal images is 24 cm, section thick-ness is 3 mm, and a 1 mm intersection gap is used.Whereas for cervical axial images the field of viewis 22 cm with a section thickness of 3 mm, and anintersection gap of 0.5 mm. A flip angle of 30� isused. For all studies, a body coil is used for the lo-calizer series, and a spinal coil is used for all othersequences.

A systematic approach to detect inci-dental findings on MRI of spine

On completion of the radiological assessment ofthe spine itself, an assessment of the paraspinalarea on the axial images is performed to assesspredominantly the abnormalities in the paraspinalmusculature. Subsequently a detailed assessmentof the organs included in the field of view on axialsections should be performed. These include, forexample, careful assessment of the pre-vertebral

Table 1 A list of frequent incidental findings that may be encountered on magnetic resonance imaging (MRI) of the spine

Part of thespine imaged

Frequently encountered incidental findings

Cervical

B Meningioma (Fig. 7)B Thyroid and salivary gland lesionB Nasopharyngeal tumour

Thoracic

B Solitary pulmonary nodule (Fig. 3)B Pleural effusionsB Interstitial fibrosis of lungsB Pneumonia

Lumbar

B Hepatobiliary: cysts, tumours (primary/secondary), gall stones (Fig. 8)B Splenic: splenunculus, splenomegalyB Renal: cysts (simple and complex), tumours (primary/secondary) (Fig. 4), hydronephrosisB Pancreatic: cysts, tumoursB Gastrointestinal: colonic carcinoma

Sacral

B Gastrointestinal: diverticulosis, rectal carcinoma (Fig. 1)B Uterine: endometrial thickening, (Fig. 5) endometrial carcinoma, leiomyoma, nabothian folliclesB Ovarian: cysts, carcinomaB Genitourinary: bladder or prostate abnormality

Ubiquitouslesions B Vascular: aortic aneurysm (Fig. 6), traumatic dissection, inferior vena cava thrombus

B Lymphadenopathy

Incidental findings on MRI of the spine 355

neck structures, particularly looking for anysignificant lymphadenopathy, mass, salivary, orthyroid lesion, and subtle nasopharyngeal abnor-mality in the cervical spine MRI. In a thoracic spineMRI, a detailed assessment of the chest wall,pleural cavities, lungs, and the mediastinum inaxial images is recommended. Retroperitoneal,intraperitoneal, pelvic organs, and the abdominalwall should be carefully assessed in the MRI of thelumbar spine. Subsequent to the assessment ofextraspinal tissues and organs on axial images, anassessment of the same should be performed onsagittal images. In the sagittal images of thecervical spine, a purposeful assessment of theintracranial structures should be performed, inaddition to the detection of any tonsillar hernia-tion. The parasagittal images are invaluable foridentifying thrombosis of the vertebral arteryparticularly in the setting of trauma. Similarly,particular care must to be taken to assess thepelvic organs, including adnexae, on the sagittalimages of the lumbar spine. The images need to be‘‘zoomed out’’ before assessing the above areas toensure that the entire field of view is reviewed.This should be followed by a detailed and purpose-ful review of the localizer/scout images. Thelocalizers are an integral part of the comprehen-sive assessment of the spinal MRI. The coronalscout images in particular offer an overall view ofthe paraspinal structures and can often confirm or

clarify the abnormality suspected on other se-quences. Pulse sequences utilized for scout seriesare typically rapidly obtained and are of lowresolution. The lesions are often obscured bysaturation bands, which are commonly used inspine imaging to suppress motion artefact fromareas anterior to the spine. Furthermore, thesections are thick, and therefore, the diseaseentity may only be visible on a single section.Even if a lesion is detected, it is often not possibleto characterize it and further imaging may benecessary.

An abnormality in the paraspinal structuresshould be sought especially when the MRI of thespine fails to explain the patient’s symptoms. Thepresent authors encountered a rectal tumour on anotherwise unremarkable lumbar spine MRI forsuspected cauda equine compromise, which ex-plained the patient’s altered bowel habits (Fig. 1).We also encountered a leiomyosarcoma in the ilia-cus muscle involving the lumbar plexus resulting inpatient’s radiating thigh pain on an MRI performedfor sciatica on the same side (Fig. 2).

The majority of the incidental MRI findingsinvolving solid organs are cysts.5,6 Cysts are com-monly seen in the kidneys, liver, adnexae, and thy-roid. Attempt should be made in these images todifferentiate simple cysts from complex cystic le-sions that require further investigation. Demon-stration of simple cyst can potentially avoid

Figure 1 A 70-year-old woman presented with lowback pain and altered bowel habits. MRI of the lumbarspine demonstrated degenerative disc disease in thelumbar spine with no significant evidence of cord orcauda equine compromise. However, detailed assess-ment of the sagittal images demonstrated a mass lesionin the lower rectum, which primarily resulted in pa-tient’s bowel symptoms. This was subsequently provento be a rectal carcinoma on histology.

356 S. Kamath et al.

further expensive and complex investigations andhelp reassure the patient. Where such differentia-tion is not possible, the incidental lesions can beassessed in the first instance with ultrasound. Pres-ence of a solid lesion on ultrasound may warrant

Figure 2 A 64-year-old woman was referred for lum-bar spinal MRI to evaluate back pain radiating to theleft thigh. Axial and coronal localizer images demon-strated an incidental left pelvic mass involving the leftiliacus muscle. Follow-up MRI of the pelvis and subse-quent CT-guided biopsy revealed a primary leiomyosar-coma. The mass was involving the lumbar plexusresulting in patient’s symptoms.

further cross-sectional imaging, such as CT orMRI, to characterize it as benign or malignant. In-cidental solid solitary liver lesions are typically be-nign.24 The vast majority of incidental adrenallesions are non-functioning adenomas.25 However,in one published series, 15e36% of treated renalcancers were found incidentally.26,27 This suggeststhat a solid or complex cystic lesion needs charac-terization preferably using CT. We have discussedbelow the imaging features of some of the com-monly encountered incidental findings during theMRI of the spine.

Cervical spine

Thyroid lesionsAlmost all (benign and malignant) thyroid lesionsshow either homogeneous or heterogeneousincreased intensity on T2-weighted images.28e30

Regions of high intensity in the thyroid on T1-weighted images may be due to haemorrhage orcolloid cyst.29,30 Adenomas tend to have distinctmargins, regular contours, and pseudocapsules,whereas papillary carcinomas may have indistinctmargins.30,31 Though a vast majority of multinodu-lar thyroid abnormality is benign, malignancy hasbeen reported in incidentally discovered solitarythyroid nodules.32 A solitary thyroid incidentallesion may need further clinical evaluation,biochemical thyroid status assessment, ultrasoundexamination, and fine-needle aspiration.32,33

Thoracic spine

Solitary pulmonary nodule (SPN)A SPN is radiologically defined as an intraparen-chymal lung lesion not bigger than 3 cm (Fig. 3). In

Figure 3 A 69-year-old male smoker presented withabnormalities of gait. Cervicothoracic MRI revealeda solitary pulmonary nodule in the right lung. This wasfurther investigated with CT.

Figure 4 A 59-year-old patient presented with lowback pain and persistent numbness in right lateral thigh.An MRI localizer image revealed a mass distorting theshape of the right kidney. A further CT confirmed thisto be an inhomogeneous mass, which was proven to berenal cell carcinoma on histology.

Incidental findings on MRI of the spine 357

general, all pulmonary nodules should be consid-ered malignant until proven otherwise. Primaryperipheral lung cancer is the most common causeof an SPN, and the probability of an SPN being ma-lignant increases with patient’s age. A spiculate,irregular margin is also highly suggestive of malig-nancy. Spiral chest CT is the ideal imaging methodto indicate the precise anatomical location anddemonstrate other pathological findings.34

Because of respiratory and cardiovascular mo-tions, low spatial resolution, and low signal tonoise ratio of the lung parenchyma, MRI spine isnot good enough to characterize a lung lesion.However, lung diseases that are associated withincreased attenuation values using CT, are alsowell visualized using MRI. Proton density is in-creased and tissueeair interfaces, which result insusceptibility artefacts, are reduced in pneumoni-tis, oedema, and carcinoma.35

Lumbosacral spine

Hepatic lesionsHepatic cysts have low signal on T1-weightedimaging and very high signal on T2-weighted imag-ing because of their fluid content. The T2 signal istypically brighter than the spleen and comparablewith the cerebrospinal fluid or bile in the gallbladder. Cysts may be indistinguishable from a hae-mangioma on T2-weighted MRI. In case of intra-cystic haemorrhage, the lesions are hyperintenseon both T1 and T2-weighted sequences and mayalso show heterogeneity, thickened wall, and fluidlevel.36

On T1-weighted images, both benign and malig-nant liver neoplasms appear hypointense relativeto normal liver. Vascular structures also appearhypointense because of flow void. Malignant he-patic lesions may also show morphological fea-tures, such as lesion inhomogeneity, centralliquefactive necrosis, unsharp outer margins, andperitumoural oedema that help to discriminatethem from benign masses.37e39 Thus, inhomoge-neous lesions have a high likelihood of malignancy,whereas markedly hyperintense lesions have a verylow probability of being malignant.40

Renal lesionsThe localizers are particularly useful for renallesions. Typically, the radiologist may identify anabnormal renal outline or mass (Fig. 4), hydro-nephrosis, or even dilated ureters on the coronalscout images. The axial sequences may add tothe information depending on the site imaged.

Simple cysts contain fluid that appears as uni-formly low signal intensity on T1 and high intensity

on T2-weighted sequences. Cysts may becomecomplicated by haemorrhage and infection, anddevelop calcification, septation, wall thickening, orhigh attenuation, features that can be shared bycystic tumours. Unless they alter the shape of thekidneys, small renal cell carcinomas can go un-detected because these lesions tend to have signalintensity similar to that of renal parenchyma onboth T1 and T2-weighted images.41e43 Five to 10%of renal cell carcinomas have a cystic appear-ance.44 Therefore, complicated or multiloculatedcysts need more attention in order to differentiatethem from cystic carcinomas.

Obstruction of the urinary flow may occur at anysite of the urinary tract. The major causes ofurinary tract obstruction vary with the age of thepatient. Calculi are most common in young adults,whereas prostatic hyperplasia or carcinoma, ret-roperitoneal or pelvic neoplasms, and calculi arethe primary causes in older patients.45

PelvisThe pelvis must be assessed carefully to identifyan incidental lesion, not only involving the pelvicorgans, but also the pelvic wall. Rectal carcinomawith overflow incontinence or retroperitonealsarcoma can be the great imitators of cord com-promise or sciatica, respectively, as demonstratedin our examples (Fig. 1 and 2).

358 S. Kamath et al.

UterusNormal endometrium is high in signal intensity onT2-weighted images. Endometrial hyperplasia usu-ally presents as diffuse thickening of the endome-trial stripe on T2-weighted images (Fig. 5). On MRI,endometrial carcinomas are characterized by en-dometrial thickening and/or an endometrialmass. Endometrial thickness of more than 4 mmthickness in postmenopausal women is consideredabnormal.46,47 Leiomyomas (fibroids) are verycommon and appear as well circumscribed, homo-geneous low signal intensity masses on T2-weighted images.48

Nabothian follicles are the most commonlyencountered benign lesions of the uterine cervix.On T1-weighted MR images, most of these lesionsare either hypointense or isointense to the cervicalstroma. On T2-weighted images, most lesions areentirely hyperintense, the walls of the cysts arethin and smooth.

Ovarian lesionsCystic lesions mostly occur in premenopausalwomen. They are mostly normal follicle cysts.Most cysts are intermediate to low signal intensityon T1-weighted images and very high signal in-tensity on T2-weighted images, reflecting theirfluid content. Most malignant tumours occur be-tween the ages of 50e70 years.49

Figure 5 An MRI for low back pain in a postmenopausalwoman revealed increased endometrial thickness. Thiswas further assessed with US and was referred to thegynaecologist to exclude endometrial carcinoma.

A single ovarian lesion with high signal intensityon T1-weighted images and high signal intensity onT2-weighted images could either represent anendometrioma, haemorrhagic cyst, or ovarianneoplasm.50,51 Endometrioma usually presents asa relatively homogeneous high signal intensitycyst on T1-weighted image and low signal on T2-weighted image, termed as shading. Haemorrhagicfunctional cysts and corpus luteum cysts have highsignal intensity on T1-weighted images. Almost alllipid containing masses within the adnexa are ter-atomas. A cystic lesion in a postmenopausalwoman especially larger than 3 cm will probablyneed further assessment to exclude malignancy.

ProstateOn T2-weighted MR images, the zonal anatomy ofthe prostate may be seen. Prostate cancer dem-onstrates decreased signal intensity within thehigh signal intensity normal peripheral zone.52,53

However, low signal intensity in the peripheralzone can also be seen in several benign conditions,such as haemorrhage, prostatitis, hyperplasticnodules, or sequelae resulting from radiation orhormonal treatment. Also T2-weighted imaginghas significant limitations for depicting cancer inthe transitional and central zones, as cancer andnormal tissues both have low signal intensity onT2-weighted images.

AortaAneurysm of abdominal aorta and thoracic aortacan be incidentally seen on MRI of the spine(Fig. 6). Sometimes the aneurysm is the real cul-prit of the patient’s back pain leading to the MRI

Figure 6 MRI of lumbar spine in an 86-year-old patientwith severe back pain and incontinence incidentallyshowed an aortic aneurysm measuring 5.4 cm indiameter.

Figure 7 A 45 year old patient presented with upperneck pain and symptoms in the right arm. MRI of the cer-vical spine demonstrated a large posterior fossa intra-cranial lesion which was subsequently proven to bea meningioma following surgery.

Incidental findings on MRI of the spine 359

examination.54,55 These should be included in thereport of spinal MRI so that appropriate follow-upor further management can be arranged.

Lymph nodesAlthough saturation band is routinely used for MRIof the spine, the pre-aortic or para-aortic lymph-adenopathy is usually not obscured and may pro-vide valuable information. This can often be thefirst sign of intra-abdominal malignancy.

Malignant lymph nodes may be hyperintenseon T2-weighted images. When necrotic, they mayappear partially or totally hyperintense on

Figure 8 A 67-year-old female patient underwent MRIfor chronic back pain. T2-weighted axial image showeda gallstone within the gallbladder.

T2-weighted images.56 Based purely on unen-hanced signal intensity, the most reliable MRI ap-pearance suggestive of nodal metastasis is a non-homogeneous signal intensity, especially onT2-weighted studies, with focal areas of highT2-weighted signal intensity within the no-de.57e59 Lymphoma produces nodes that arehomogeneous and clearly delineated, like hyper-plastic adenopathy. If lymph nodes are affectedby bacteria, such as tuberculosis or Staphylococ-cus, there may be liquefaction or necrosis. Theseappearances are similar to the metastasis ofsquamous cell carcinomas or post-radiotherapyor chemotherapy.56

Conclusion

Incidental findings are common in the MRI imagesof the spine. The implementation of PACS hasresulted in increased detection of these incidentalabnormalities due to the availability of uncroppedand localizer images for reporting. These inciden-tal findings may be more significant than the spinalproblems being evaluated and can have significantimpact on patient management and medicolegalimplications to the radiologist. The onus is on theradiologist to detect, characterize, and report anyrelevant incidental findings. A systematic ap-proach to the MRI of the spine should includeassessment of tissues and organs outside the regionof clinical interest to detect any incidental abnor-mality. Particular attention should be paid to thelocalizer images. The radiologist needs to makea judgement for the need and the appropriatepath of further management often from limitedimages of the organ concerned or low-resolutionlocalizer images.

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