Computed Tomography of the Brain Stem with Intrathecal Metrizamide.

Transcription

1 Computed Tomography of the rain Stem with Intratheal Metrizamide. Part II: Lesions in and around the rain Stem 13 Mihel E. Mawad 1. John Silver Sadek K. Hilal S. Ramaiah Ganti The pratial usefulness of omputed tomography with intratheal metrizamide in imaging the brain stem is illustrated in six examples where the lesions were misdiagnosed on intravenously enhaned omputed tomography, angiography, or air study. Foal and diffuse atrophi hanges of the brain stem were demonstrated in symptomati patients where none of the other radiographi or linial investigations were onlusive. Metrizamide omputed tomography is probably the most sensitive method for imaging lesions in and around the brain stem and erebellopontine angle. The appliation of the anatomi detail desribed in part 1 of this paper (in this issue) an be illustrated by a few linial examples in whih the orret diagnosis was reahed only by omputed tomography (CT) with intratheal metrizamide. In these ases, onventional studies were either inomplete, falsely positive, or falsely negative. While onventional CT with intravenous ontrast material an demonstrate abnormalities in brain stem density, metrizamide isternography shows th e subtle hanges in brain stem shape and surfae features. For des riptive purposes, we lassified the morphologi hanges of the abnormal brain stem into three ategories: (1) expansion and deformity of the brain stem by intraaxial masses; (2) distortion and displaement of the brain stem by pressure from extraaxial masses, and (3) generalized and foal atrophi hanges. bnormalities of the rain Stem Intraaxial Mass This artile appears in the January / February 1983 issue of JNR and the Marh 1983 issue of JR. Reeived Marh ; aepted after revision September 10, 1982 ' ll authors: epartmenl of Radiology, Neurologial Institute, Columbia-Presbyteri an Medial Center, 710 W. 168th St., New Yo rk, NY ddress reprint requests to M. E. Mawad. JNR 4:13-19, January / February / 83/ $00.00 merian Roentgen Ray Soiety Intraaxial masses an produe the following hanges: (1) obliteration of th e surfae features of the medulla, espeially with the loss of bil ateral onave symmetry and blunting of the sul i; (2) flattening and bakward displ aement of the fourth ventrile with blunting of the median sulus; and (3) persistent unilateral enlargement of the medulla, pons, midbrain, or any of the erebell ar pedun les [1 ]. generalized inrease in the size of the medulla without deformity of its shape is not likely to our. Previous radiologi measurements of the various diameters of the brain stem are useful only in the late ondition (e.g., after the overall size of the medulla has already in reased). Earli er hanges ourring in th e brain stem are the loss or deformity of loal surfae features. Hene, metrizamide CT isternography is potentially a ve ry sensitive test for th e early diagnosis of intraaxial brain stem lesions. Extraaxial Mass Extraaxial masses in the posterior fossa an be outlined diretly by metrizamide

2 14 MW ET L. JNR:4, Jan./ Feb Fig. 1.- Case 1. Intraaxial brain stem mass and bilateral aousti tumors deteted only on metrizamlde CT., Conve ntional isternogram. Norm al fourth ventrile ( arrows)., CT with intravenous ontrast was not helpful. C, Metrizamide CT. Large losed medulla at foramen magnum with obliteration of pre- and postolivary suli and strething of hypoglossal rootl ets ( arrows)., Open medulla has lost its harateri sti quadrionave appearane. E, Obliteration of median sulus (long arrow) and medial eminene in floor of fourth ventrile. ilateral aousti tumors (short arrows ) olude eah internal auditory anal. E CT of th e subarahnoid spae. This method is partiularly helpful in distinguishing between an exophyti brain stem glioma and an extraaxial neoplasm. It is al so very useful in differentiating between a small neoplasm and a normal struture! (e.g., between an aousti neuroma and the floulus). rain stem hanges seondary to an extraaxial mass inlude pressure deformity, shift, and displaement. trophi Changes trophi hanges of th e brain stem are of two types: (1) Generalized atrophy produes a rel ative enlarg ement of all surrounding subarahnoid spaes and of th e fourth ventrile. ll suli and fi ssures on th e surfae of the brain stem are preserved and exaggerated, parti ul arly th e ventral median fissure and th e ventrolateral sulus. (2) Foal atrophy may result from foal pressure by an extraaxial mass or a tortuous vessel, a loal vasul ar aident, or a primary degenerative proess involving trats or nulei. Metrizamide CT isternography is uniquely abl e to provide information that an be orrelated with the linial findings; it is unsurpassed in showing general or foal brain stem atrophy. Representative Case Reports Case 1. Intraaxial brain stem glioma and bilateral aousti tumors demonstrated only on metrizamide CT. Conventional isternogram and intravenous ontrast-enhaned CT were normal. 15'i2-year-old patient presented with brain stem symptoms, bilateral hearing loss, paralysis of th e voal ords, and faial paralysis. The onventional isternogram showed a norm al, nondisplaed fourth ventrile (fig. 1 ). The CT san with intravenous ontrast was not helpful (fig. 1 ). The metrizamide CT isternogram demonstrated a ballooned losed medulla with omplete obliteration of th e ventral fi ssure and anterolateral sulus (fig. 1 C). The rootl ets of th e hypoglossal and first ervial nerves were strethed. There was obvious loss of the bilateral onavity of the open medulla. The features of th e fl oor of the fourth ventrile were ompletely obliterated beause of the infiltrating tumor (fig. 10). The higher setions showed bilateral aousti neuromas filling the internal auditory anals and protruding into the erebellopontine angle isterns (fig. 1 E). Case 2. Intraaxial neoplasm in the brain stem and ervial spinal ord shown in its entirety in a single study. 47-year-old man had brain stem symptoms inluding ataxia, vertigo, vertial nystagmus, and right faial weakness. The angiogram (fig. 2) showed evidene of a mass effet in the pons and medulla. Th e metrizamide CT delineated the intraaxial tumor in th e pons (fig. 2) and medulla (fig. 2C) and also showed the lower extension of the tumor into the ervial ord, whih was expanded down to the C5 level (fig. 20). ordingly, the radiotherapy portal was extended to over the entire tumor. myelogram would have outlined the ervial omponent of th is lesion. seond study would have been neessary to outline the extent of the intraranial omponent. Metrizamide CT istern ography outlined the entire tumor.

3 JNR:4, Jan./Feb CT OF RIN STEM LESIONS 15 Fig. 2.- Case 2. Intraaxial brain slem neoplasm exlending inlo spin al ord., Vertebral angiogram shows posterior displaemenl of retromedullary segmenl of poslerior inferior erebell ar arlery (arrows l. 6-0, Metrizamide CT. iffuse swelling of pons, medulla, and ervi al ord down to C5. Entire extent of lesions was demonstrated on single study. Case 3. n exophyti intraaxial brain stem tumor presenting by onventional CT as an extraaxial mass. 30-year-old woman had oasional episodes of left faial numbness, dereased taste sensation, dereased left orneal refl ex, and horizontal nystagmus on lateral gaze. The onventional CT san after intravenous ontrast enhanement showed an enhan ing extraaxial mass in the left erebellopontine angle region with a questionable intraaxial omponent (fig. 3 ). The metrizamide study showed the presene of an intraaxial brain stem tumor extending from the losed medulla to the superior olliular level of th e mesenephalon. The losed medulla was expanded and had lost its surfae features (fig. 3 8). The fourth ventrile was distorted and devi ated toward the right; the left brahium pontis was swollen (fig. 3C). The higher setions showed asymmetry of the erebral pedunles with fl attening of the left lateral mesenephali su l us and expansion of th e left erebral pedun le as well as the left superi or olliulus (fig. 3 ~ ). In addition, th ere was a filling defet in th e interpedunular fossa d ue to an exophyti omponent ari sing from the mamillary bodies and projeting downward into the istern. Case 4. Generalized atrophy of the brain stem seondary to viral meningoenephalitis. 47-year-old man had a proven viral meningoenephalitis th at left him w ith partial deafness and a onstant noise in the ri ght ear. He subsequently presented w ith intermittent diplopia on downward gaze, diffuse hyperreflexia, and left arm weakness. His erebrospinal fluid (CSF) was negative for oligo lonal bands. The onventional CT san (fig. 4) showed a large isterna magna and a apaious fourth ven tri le. Metrizamide CT isternography showed an atrophi losed medulla (fig. 48) with a narrow transverse diameter and effaed pyramidal protuberane; th ere was also unusual prominene of the dorsal median fi ssure. The isthmus of the pons was atrophi with a large upper fourth ventrile and attenu ated brahium onjuntivum bilaterally (fig. 4C). The erebral aquedut was strikingly d ilated and the erebral pedunles were small relati ve to the size of th e midbrain (fig. 40). While the exat etiology of these strutural hanges in th e brain stem remains un lear, one an relate them to th e previous episode o f meningoenephalitis. The atrophy demonstrated on onventi onal CT is not an unommon finding ; the metrizamide study, however, reveals in great detail the extent of the pronouned atrophi hanges th at mat h th e linial findings. Case 5. Normal brain stem in whih a pneumoenephalogram and onventional enhaned CT san were falsely positive for a brain stem mass. 60-year-old woman had dysphagia, tongue immobility, hoarseness, and right abduens nerve palsy. The diagnosis of brain stem glioma was suspeted on the basis of the linial findings. The onventional CT san (fig. 5) and the pneumoenephalogram (fig. 58) suggested a brain stem mass with enlargement of th e pons and lower medulla and bakward d isplaement of the fourth ven tri le. Metrizamide CT, however, showed a rath er apaious fourth ventrile with preservation of the median su l us and no evidene o f a spae-oupying lesion or mass effet (fig. 5C). The pons and both brahium pontii were unremarkable (fig. 50). Further li nial and

4 16 MW ET L. JNR:4, Jan./ Feb Fig Case 3. Inlraaxial tumor of brain stem demonstrated by metrizamide CT while onventional CT suggesled an extraaxial mass., Enhaning mass in left erbellopontine angle appears mostly extraaxial extending through in isura (blak arrows ). Enhaning nodule (white arrows ) is adjaent to displaed fourth ventrile., Metrizamide CT at losed medullary level. Enlarged medulla has lost its surfae features (arrows ). C, Fourth ventrile is shifted (arrow) and left brahium pont is is swollen., Metrizami de surrounds swollen and deformed midbrain with fl attening of lateral mesenephali sulus ( unrossed arrow) showing true intraaxial nature of lesion. tnvolvement of mammillary bodies behind opti hasm (rossed arrows ). laboratory workup revealed the diagnosis of mu ltiple slerosis with orresponding CSF find ings. Th e misleading findings on pneumoeneph alography were probably the result of a menisus formation between the air and CSF around the floor of the fourth ventrile. Case 6. Loal atrophi hanges of th e brain stem and its deformity by adjaent tortuous vasular strutures. 59-year-old man with malignant hypertension had a 10 year history of left lower motor neuron faial nerve palsy and omplete deafn ess of the left ear. Th e rest of his ranial nerves were normal. The admitting linial diagnosis was a tumor in the left ere bellopontine angle. The metrizamide istern ogram (figs. 6 6 and 6C) showed a tortuous vertebral basilar artery on th e left sid e ausing an atrophi extrinsi pressure deformity on th e medullary pontine segment and the left brahium pontis at the level of origin of th e seventh and eighth nerves. The rest of the brain stem was normal (figs. 6 and 60). This examinati on unequivoally ruled out an intraor extraaxial tumor and at the same time offered an explanation for th e pati ent's dereased hearing and faial palsy. The evaluation of foal atrophi hanges and pressure effets by vasular strutures is probably impossible to obtain with other radiographi methods, inluding CT with air ontrast, beause these offer a limited vi ew of th e anatomy. isussion Metrizamide CT isternography has rapidly repl aed both angiography and pneumoenephalography at our institution for the evaluation of brain stem pathology. Most brain stem gliomas are astroytomas [2] that infi ltrate in a diffuse and insidious fashion, seldom ausing loalized mass effet or abnormal vasularity on angiography. When they displae vessels, however, they are usuall y eentri and have reahed an advaned stage [3]. We find the new imaging method very rel iable and sensitive to early hanges and subtle deformities of the brain stem that an be easily overlooked with other diagnosti proedures inluding CT enhaned with intravenous ontrast media. In the group of patients who liniall y appear to have slowly developing brain stem lesions with ranial nerve and long trat signs, the diagnosti workup should inlude a metrizamide CT isternogram despite " normal" onventional investigations. In a study performed by uoulay and Radu [4] with vertebral angiography, air studies, and onventional CT, before the use of metrizamide, less than 10% (5 / 59) of their patients had a " diagnosti" investigation. In our series of 10 ases of brain stem masses either suspeted or diagnosed on routine CT, vertebral angiography, or air studies, metrizamide not only onfirmed the presene of the neoplasm but also aurately demonstrated a level of extension (e.g., into the midbrain) that would not have been suspeted otherwise. In addition, it offered good display of the ervial ord for evaluation of audal extension of the lesion or a possible oexisting syringomyeli avity.

5 JNR :4, Jan./Feb CT OF RIN STEM LESIONS 17 Fig. 4.- Case 4. Generalized brain stem atrophy optimally demonstrated by metrizamide CT., Capaious fourth ventrile with prominent isterna magna., Metrizamide CT of losed medull a. Prominent dorsal median fissure (unrossed arrow) and ehaed pyramidal protuberane (rossed arrow). C, Isthmus of pons. Large upper fourth ventrile and small attenuated brahium onjuntivum ( arrows )., Upper mesenephalon. Cerebral aquedut is unusually large (long arrow) and erebral pedunles are small ompared with body of midbrain. Lateral mesenephali sulus is prominent ( short arrows). rnold Chiari malformations are ideally evaluated with this method [5]. The foramen magnum, med ulla, and erviomedullary juntion, as well as the position of the erebell ar tonsils and the shape and loation of the fourth ventrile, are demonstrated in great detail. Cerebellopontine angle lesions suh as small or intraanaliular aousti neuromas are also best studied with metrizamide CT isternography. This inludes the evaluation of ranial nerve syndromes presumed seondary to a tortuous basilar artery. lthough CT enhaned with intravenous ontrast media demonstrates the abnormal etati vessels [6], metrizamide shows to better advantage the resulting deformity of the brain stem and helps to exlude a oexisting neoplasm. CT of the erebellopontine angle with air ontrast is useful for the demonstration of small aousti neuromas provided that hearing loss an be preditably attributed to a neuroma; other auses of deafness should be rul ed out linially. Transverse and sagittal linear measurements of the brain stem, both on CT with intravenous ontrast [7] and CT isternography [8], have been proposed in the evaluation of displaement of the fourth ventrile and swelling of the surrounding strutures. We find that standardized measurements are diffiult to obtain and fi xed anatomi landmarks are often elongated or hard to reprodue. l so, a signifiant range of variation in normal values exists, thus preluding the detetion of early swelling or atrophy by measurements alone. Instead, we rely mostly on the fine morphologi details desribed in part 1 of this paper, and we onsistently try to reognize the different eminenes, fi ssures, and sul i in ord er to detet asymmetry, distortion, or exaggeration of surfae grooves. The use of ai r as a ontrast agent for CT is inadequate for the demonstration of surfae features of the brain stem beause of partial filling of the isterns and menisus formation that preludes a detailed outline. High-reSOlution sanning using primary reonstrution and thin tomographi setions of no more than 5 mm thikness are a neessity. l so, onseutive sans should not be spaed more than 5 mm apart, espeiall y around the medulla. To redue the morbidity of metrizamide we limit the onentration to an isotoni 170 mg / ml ; however, newer nonion i aq ueous media with less neurotoxiity than metrizam ide [9] will undoubtedly enourage and failitate the use of CT isternography. Conlusion Our urrent impression is that metrizamide CT is exellent for imaging th e brain stem in the evaluation of both intraand extraaxial lesions. We find it superior to pneumoenephalography, angiography, and routine ontrast-enhaned CT, although the latter proedure should be th e

6 18 MW ET L. JNR:4, Jan./Feb Fig Case 5. rainstem tum or suspeted on onventional CT and air study proven norm al on metrizamide CT., Fourth ventrile appears displaed on routine CT ( arrows )., Pneumoenephalogram. pparent posterior displaement of floor of fou rth ventrile at level of medulla (arrows). C, and, Metrizamide CT. Norm al median sulus in floor of fourth ventrile (arrow ) and normal pons. o Fig Case 6. Foal atrophi hanges demonstrated by metrizamide CT., t level of open medulla. Normal brain stem and erebell ar hemispheres., Left eighth nerve (long arrow ) is onsistently smaller th an right ( short arrows ) on all setions. Left vertebral artery is larg e and tortuous and appears to be pressing on eighth nerve (rossed arrow). C, Extrinsi pressure deformity on lef1 brahium pontis and medullary-pontine juntion ( urved arrow) aused by tortuous basilar artery (straight arrow)., t level of pons. Normal pons. eafness and faial palsy are expl ainable by tortuous vertebral artery. o

7 JNR:4, Jan. / Feb CT OF RIN STEM LESIONS 19 initial study and angiography is often omplementary. In the ase of brain stem tumors, metrizamide isternography will aurately define the vertial extension into the mesenephalon or the upper ervial ord. Extraaxial masses are readily identified and easily differentiated from intraaxial tumors. Posterior fossa vessels and ranial nerves are both demonstrated aurately. This imaging method is ideally suited for the evaluation of syndromes attributed to neural pressures aused by tortuous vessels. The unique value of metrizamide isternography, however, is the detetion of foal or generalized atrophy in the brain stem, espeially in patients with long trat signs, ranial nerve symptoms, or both. The linial and radiologi workup in this group of patients has heretofore been frustratingly negative or inonlusive. REFERENCES 1. rayer P, Rosenbaum E, Reigel, ank WO, eeb ZL. Metrizamide omputed tomography isternography: pediatri appliations. Radiology 1977;124: Golden GS, Ghatak NR, Hirano, et al. Malignant glioma of the brain stem. linio-pathologial analysis of 13 ases. J Neurol Neurosurg Psyhiatry 1972;35: Seeger JF, Gabrielsen TO. ngiography of eentri brain stem tumors. Radiology 1972; 105 : uoulay GH, Radu EW. How should one investigate th e posterior fossa? Neuroradiology 1978;15 : Forbes WStC, Isherwood I. Computed tomography in syringomyelia and the assoiated rnold Chiari type I malformation. Neuroradiology 1978;15 : eeb Z, Jannetta P, Rosenbaum, Kerber C, rayer. Tortuous vertebrobasilar arteries ausing ranial nerve syndromes: Sreening by omputed tomog raphy. J Cornput ssist Tornogr 1975;3: ilaniuk LT, Zimmerm an R, Littman P, et al. Computed tomography of brain stem gliomas in hildren. Radiology 1980; 134: Steele JR, Hoffman JC. rain stem evaluation with CT isternography. JNR 1980;1 : , JR 1981 ;136: Hopkin s RM, dams M, Lau HM, Creighton JM, Hoey G. logluomide: a new non ioni myelographi agent. Prelinial studies. Radiology 1981;140: