mri of cranial nerve enhancement · mri of cranial nerve enhancement ... characterizing dise ase of...

AJR:185, December 2005 1487

AJR 2005; 185:1487–1497

0361–803X/05/1856–1487

© American Roentgen Ray Society

Saremi et al.MRI of Cranial Nerve Enhancement

N e u ro r a d i o l o g y • P i c t o r i a l E s s ay

MRI of Cranial Nerve Enhancement

Farhood Saremi1

Mohammad Helmy1

Sahar Farzin1

Chi S. Zee2

John L. Go2

Saremi F, Helmy M, Farzin S, Zee CS, Go JL

DOI:10.2214/AJR.04.1518

Received September 25, 2004; accepted after revision March 7, 2005.

1Department of Radiological Sciences, University of California, Irvine, 101 The City Dr., Rte. 140, Orange, CA 92868. Address correspondence to F. Saremi ([email protected]).

2Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, CA.

OBJECTIVE. In this pictorial essay, we review the MR appearance of cranial nerveenhancement in a variety of entities including neoplastic, infectious, and idiopathicdiseases.

CONCLUSION. MRI with contrast enhancement is a valuable tool for detecting andcharacterizing disease of the cranial nerves. Abnormal cranial nerve enhancement on MRI maysometimes be the first or only indication of an underlying disease process.

RI is invaluable in characterizingdisease of the cranial nerves. Ga-dolinium administration in-creases the ability of MRI to de-

tect such abnormalities. We begin thispictorial essay with a description of the his-tologic anatomy of the cranial nerves andpatterns of normal cranial nerve enhance-ment. After briefly discussing the patho-physiology, we review the MR appearance ofabnormal cranial nerve enhancement in var-ious diseases ranging from common neo-plastic and infectious conditions to rare con-ditions such as ophthalmoplegic migraineand idiopathic pachymeningitis. In somecases, abnormal cranial nerve enhancementon MRI may be the only clue to the underly-ing disease.

Anatomy and PathophysiologyThe cranial nerves are surrounded by a

series of connective tissue sheaths called en-doneurium, perineurium, and epineurium.The blood–nerve barrier of cranial nerves ismaintained by the combined actions of tightjunctions in the endothelium of the endo-neural capillaries and tight junctions in theinner layers of the perineurium. Various in-sults disrupt the blood–nerve barrier, allow-ing leakage and accumulation of contrastmaterial with resultant perineural enhance-ment. Such disruption may arise secondaryto neoplasm, autoimmune disease, inflam-mation, demyelination, ischemia, trauma,radiation, and axonal degeneration, all re-sulting in abnormal cranial nerve enhance-ment (Appendix 1).

Normal Cranial Nerve EnhancementThere are instances of normal cranial

nerve enhancement. The geniculate, tym-panic, and mastoid segments of the facialnerve possess peri- and epineural venousplexuses that may cause moderate enhance-ment by an increased vascular pool of con-trast material [1]. The intracanalicular–laby-rinthine segment does not normally enhance.The trigeminal ganglion and the proximalportions of its divisions are seen as discretenonenhancing structures surrounded by anenhancing perineural vascular plexus. En-hancement of the trigeminal ganglion or itsmaxillary or mandibular divisions is infre-quently seen as evidenced by their avascularappearance in cadaveric specimens [2].When such enhancement is seen on MRI, itmay be related to suboptimal imaging pa-rameters, avid enhancement of the perivas-cular plexus, or a combination of both.

NeoplasmNeoplastic meningitis refers to the dis-

seminated seeding of the leptomeninges bymalignant cells. This includes carcinoma-tous meningitis in patients with solid tumorsand lymphomatous and leukemic meningitiswhen involvement is related to these under-lying diseases. The most common cancers toinvolve the leptomeninges are breast (5%),lung (9–25%), and melanoma (23%) [3](Fig. 1). MRI findings include pial enhance-ment and nodularity, smooth or nodular cra-nial nerve enhancement, hydrocephalus,and coexisting brain or bone metastases [4].Primary diffuse leptomeningeal gliomatosis

M

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1488 AJR:185, December 2005

is a rare condition whereby a glioma arises fromheterotopic cell nests in the leptomeninges.Leptomeningeal dissemination is an un-

common complication of gliomas andother primary intraaxial malignancies.The presence of a single unexplained en-

hancing cranial nerve in a patient with cancerraises the possibility of leptomeningealdissemination.

A B

C D

Fig. 1—48-year-old woman with metastatic melanoma and meningeal carcinomatosis.A–E, Contrast-enhanced axial (A, B, D, and E) and coronal (C) T1-weighted images show enhancement and involvement of multiple cranial nerves: oculomotor nerves (arrows, A); trigeminal nerves (arrows, B); complex of seventh and eighth cranial nerves (arrows, C); complex of ninth, tenth, and eleventh cranial nerves (long arrows, D and E); and hypoglossal nerves (short arrows, E).

E



A

Fig. 2—56-year-old woman after resection of adenoid cystic carcinoma of right hard palate.A, Axial bone window CT image shows widening of right pterygopalatine fossa (arrow).B and C, Contrast-enhanced axial T1-weighted MR images reveal infiltrating mass in right pterygopalatine fossa (short arrow, B) and cavernous sinus (short arrow, C). Note abnormal signal intensity in right masticator space (long arrows, B) and right medial temporal lobe (long arrows, C).

B C

A

Fig. 3—43-year-old man with acute lymphoblastic leukemia.A, Axial FLAIR image reveals leukemic infiltrate of left pons and brachium pontis (arrow).(Fig. 3 continues on next page)

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Perineural tumor extension, a form ofmetastatic disease, involves the spread ofprimary mucosal or cutaneous tumors tononcontiguous regions along nerve sheaths.Perineural tumor spread has been shown inperineural or endoneural tissue planes alonga path of least resistance. Retrograde spreadis significantly more common than ante-

grade spread. A series by Parker and Harns-berger [5] found perineural spread occursmost commonly with squamous cell carci-noma and adenoid cystic carcinoma, withthe facial nerve and second and third divi-sions of the trigeminal nerve most fre-quently involved (Fig. 2). Other neoplasticand aggressive infectious processes, such as

acute lymphoblastic leukemia, non-Hodgkin’s lymphoma, malignant schwan-noma, aspergillosis, mucormycosis, and ac-tinomycosis, also show perineural extension(Fig. 3). MRI findings of perineural involve-ment include smooth thickening and en-hancement of the nerve, concentric expan-sion of the skull base foramina with

B C

Fig. 3 (continued)—43-year-old man with acute lymphoblastic leukemia.B and C, Contrast-enhanced axial T1-weighted images show antegrade perineural extension along course of left spinal trigeminal tract and nuclei (arrow, B) into preganglionic segment of left trigeminal nerve (arrow, C).

A B

Fig. 4—7-year-old girl with tuberculous meningitis.A and B, Contrast-enhanced axial (A) and coronal (B) T1-weighted images show abnormal peripheral enhancement of oculomotor nerves (long arrows). In addition, there is leptomeningeal enhancement of anterior surface of brainstem (short arrows, A).



obliteration of normal fatty contents, en-largement of the cavernous sinus, and neu-ropathic muscular atrophy [6].

InfectionInfectious meningitis results from viral,

bacterial, fungal, or parasitic infection. Lep-

tomeningitis is the most common form of in-tracranial tuberculosis, particularly in the pe-diatric population. Cranial nerve involvement

Fig. 5—32-year-old man with cryptococcal meningitis and perioptic neuritis. Contrast-enhanced axial T1-weighted image with fat suppression reveals thickening and enhancement of perineural structures of left optic nerve.

A B

Fig. 6—61-year-old man with perineural spread of rhinocerebral mucormycosis who presented for follow-up after right orbital exenteration.A and B, Axial T2-weighted (A) and contrast-enhanced T1-weighted (B) images show recurrence of infection with invasion of right cavernous sinus (long arrows, A) and retrograde involvement of trigeminal nerve along cavernous, ganglionic, and cisternal segments (arrows, B). Abnormal signal within right pons indicates edema (short arrow, A).

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is seen in 17–70% of patients and occurs inthe setting of diffuse leptomeningeal tubercu-losis. Impairment has been attributed to is-chemia of the nerve or entrapment of thenerve in basal exudates [7] (Fig. 4).

Cryptococcus neoformans is the mostcommon fungus to involve the CNS. Cryp-tococcal meningitis is one of the typicalpathologic manifestations and can result inoptic neuropathy in both immunocompetentand immunocompromised patients (Fig. 5).

Optic neuropathy is a rare complication ofcryptococcal meningitis and usually occursin non-AIDS patients. Necrosis of the opticnerves and infiltration of the meningesaround the optic tracts, nerves, and chiasmby cryptococcal organisms have beenobserved [8].

Rhinocerebral mucormycosis is a poten-tially devastating fungal infection in diabeticand immunocompromised patients. Sinonasaldisease often progresses to the orbit and

cavernous sinus and may be complicated byvascular and perineural invasion and localthrombotic infarction [9] (Fig. 6).

Cranial neuroschistosomiasis occurs lesscommonly than the spinal variety and mayarise with any of the clinical forms of thisparasitic infection. Eggs within the CNSinduce a cell-mediated periovular granulo-matous reaction that leads to signs andsymptoms of increased intracranial pressureand focal neurologic signs [10]. Although

A B

C

Fig. 7—17-year-old boy with neuroschistosomiasis. Contrast-enhanced T1-weighted images show range of involvement of CNS in schistosomiasis.A, Sagittal image shows enhancing masses within chiasmatic–hypothalamic (short arrow) and pineal (long arrow) regions.B, Coronal image shows thickened and enhancing trigeminal nerves (arrows).C, Axial image reveals enhancing mass (arrow) in right cerebellopontine angle with extension into internal auditory canal.



meningeal spread of infection involvingcauda equina nerve roots has been reported,rare instances of cranial nerve involvementmay also be seen as in our case (Fig. 7).

Cranial neuritis in Lyme disease may in-volve any of cranial nerves III through VII,with the facial nerve most frequently af-fected and often associated with cochleoves-tibular nerve abnormalities. The affectedsegments appear thickened and enhance.Viral infections related to herpes simplex vi-rus type 1, cytomegalovirus, and Varicellazoster organisms also manifest with cranialnerve involvement and show abnormal en-hancement on MRI.

Postinfectious and Demyelinating Disorders

Bell’s palsy is the most common cause ofunilateral peripheral facial neuropathy. In ad-dition to normal enhancement of the facialnerve segments discussed earlier, there ispathologic enhancement of the intracanalicu-lar–labyrinthine portion (Fig. 8). Martin-Du-verneuil et al. [11] suggest three criteria forpathologic enhancement of the facial nerve:enhancement outside the facial canal, exten-sion of enhancement to cranial nerve VIII,and intense enhancement of the labyrinthineand mastoid segments. In Ramsay Hunt syn-drome, abnormal facial nerve enhancement is

accompanied by enhancement of the vestibu-lar and cochlear nerves as a result of exten-sion of inflammation from cranial nerve VIIto the intracanalicular portions of these cra-nial nerve VIII divisions.

Ophthalmoplegic migraine is a rare condi-tion characterized by headache and oculo-motor nerve palsy lasting days to weeks.MRI findings include reversible enhance-ment of the cisternal segment of the oculo-motor nerve and focal thickening at the exitof the nerve in the interpeduncular cistern(Fig. 9). Involvement of cranial nerves IV,V1, and VI also occurs. Multiple cranialnerve involvement is also present in a group

A B

C

Fig. 8—32-year-old man with Bell’s palsy.A–C, Contrast-enhanced axial (A) and coronal (B and C) T1-weighted images show abnormal enhancement of right facial nerve extending from distal intracanalicular segment (arrows, A and B) to distal mastoid segment (arrow, C).

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of inflammatory demyelinating polyneurop-athies that include Guillain-Barré and vari-ants, such as Miller Fisher syndrome andpolyneuritis cranialis.

GranulomatosisIntracranial neurosarcoidosis has a predi-

lection for the basal leptomeninges, andinvolvement of every cranial nerve has beendescribed. MRI shows a spectrum of CNSabnormalities including diffuse or nodularthickening and abnormal enhancement ofthe leptomeninges in the basal cisterns andhypothalamic regions [12] (Fig. 10).Perineural spread has also been reported insarcoidosis [13]. Clinical involvement and

imaging cranial nerve involvement fre-quently do not coincide, and clinical resolu-tion may not imply imaging resolution [14].

Idiopathic hypertrophic cranial pachy-meningitis is a rare disease characterizedby inflammation and fibrosis of the duramater. It remains a diagnosis of exclusionbut may be the presenting manifestation ofgranulomatous diseases such as sarcoido-sis, Wegener’s granulomatosis, or tubercu-losis. MRI shows focal or diffuse thicken-ing and enhancement of the dura thatencase cranial nerves causing recurrentcranial neuropathies. The oculomotor, ab-ducens, and facial nerves are more fre-quently involved [15].

Tolosa-Hunt syndrome consists of painfulophthalmoplegia related to a granulomatousinflammatory process in the cavernous si-nus. MRI findings are nonspecific and in-clude enhancement and abnormal soft tissuein the ipsilateral cavernous sinus and orbitalapex [16] (Fig. 11).

Postradiation NeuritisRadiation-induced cranial nerve injury is

an uncommon, usually delayed, complicationof radiation therapy or radiosurgery. Cranialnerve deficits may be permanent or resolvespontaneously. Loss of the nerve–blood bar-rier due to demyelination and ischemia, coag-ulation necrosis, or peripheral fibrosis results

A B

C

Fig. 9—57-year-old man with ophthalmoplegic migraine.A–C, Unenhanced axial (A) and enhanced axial (B) and coronal (C) T1-weighted images reveal smooth enlargement and homogeneous enhancement of cisternal segment of left oculomotor nerve (arrows).



in cranial nerve enhancement. Radiation-induced optic neuropathy occurs months toyears after exposure of the anterior visual

pathways to ionizing radiation. MRI showssmooth enlargement and enhancement of theoptic nerve and chiasm (Fig. 12).

Primary Nerve TumorsVestibular schwannomas are the most com-

mon cranial nerve schwannomas, followed by

Fig. 10—58-year-old man with neurosarcoidosis.A and B, Contrast-enhanced axial T1-weighted images show enhancement and involvement of cisternal segments of right and left seventh and eighth cranial nerve complexes (arrows, A) and root entry zones of preganglionic trigeminal nerves (arrows, B).

BA

A B

Fig. 11—35-year-old woman with Tolosa-Hunt syndrome presenting with painful ophthalmoplegia.A, Enhancement and enlargement of left cavernous sinus are illustrated on contrast-enhanced coronal T1-weighted image (arrow).B, Extension of enhancing tissue into left orbital apex (arrow) is seen on contrast-enhanced axial T1-weighted image.

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trigeminal and facial schwannomas and thenglossopharyngeal, vagus, and spinal accessorynerve schwannomas (Fig. 13). Neurofibroma-tosis 2 is characterized by bilateral vestibularschwannomas. Schwannomas of the other cra-nial nerves occur more frequently in neurofi-bromatosis 2. Enhancing hemangiomas, men-ingiomas, or metastases may mimic theappearance of early schwannomas.

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A B

Fig. 13—48-year-old woman with schwannoma arising from left inferior vestibular nerve.A and B, Contrast-enhanced axial (A) and coronal (B) T1-weighted images show small enhancing tumor (arrows).



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APPENDIX 1: Classification of Cranial Neuropathies

Neoplastic: Carcinoma, lymphoma, leuke-mia, glioma, myeloma

Infection: Tuberculosis, syphilis, lep-rosy, mycoplasma, Lyme disease, viralinfections, fungal infections, parasiticinfections

Postinfectious and demyelinating: Bell’spalsy, Ramsay Hunt syndrome, ophthalmople-

gic migraine, Miller Fisher syndrome, poly-neuritides, multiple sclerosis

Granulomatosis: Sarcoidosis, idiopathicgranulomatosis, vasculitis, inflammatory gran-ulomatosis

Angiopathic: Wegener’s granulomatosis,Churg-Strauss syndrome, Behçet’s syndrome,diabetes

Idiopathic: Idiopathic pachymeningitis,Tolosa-Hunt syndrome

Physical or chemical: Radiation, trauma,surgery, toxins, drugs

Hereditary: Dejerine-Sottas disease, Krabbe’sdisease

Primary nerve tumors: Schwannoma, neu-rofibromatosis

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