Comparison of MR Imaging, CT, and Angiography in the Evaluation of the Enlarged Cavernous Sinus

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1 907 Comparison of MR Imaging, CT, and ngiography in the Evaluation of the Enlarged Cavernous Sinus William L. Hirsh, Jr.' Frank G. Hryshko' Laligam N. Sekhar2 James runberg' Emanuel Kanal' Rihard E. Lathaw' Hugh Curtin' Twenty-one patients with enlargement of the avernous sinus were studied with CT and MR imaging. Eighteen of the patients also had erebral angiography. MR was superior to CT in differentiating parasellar aneurysms from neoplasti masses. MR was also superior to both CT and angiography in defining the relationships of avernous sinus neoplasms to the internal arotid artery, pituitary gland, opti hiasm, infundibulum, and fifth ranial nerves. Only in the definition of bone erosion or hyperostosis was MR inferior to another method (CT). We onlude that MR should be the initial diagnosti study in patients with symptoms of a parasellar mass, with supplementation when neessary by CT and angiography. The anatomy of the avernous sinus is omplex and has been reviewed reently [1, 2]. In the past, masses of the avernous sinus were rarely treated surgially beause of potential bleeding from the avernous venous plexus; injury to the internal arotid artery; or damage to ranial nerves III, IV, or VI. New surgial approahes, use of the surgial mirosope, and intraoperative eletromyographi monitoring of ranial nerve funtion have failitated the surgial management of avernous sinus lesions [3, 4]. The radiographi evaluation of patients with a suspeted parasellar lesion is direted toward deteting the mass, determining if the mass is an aneurysm or neoplasm, and, if neoplasti, determining the relationship of the mass to surrounding strutures. It is partiularly important to differentiate neoplasti masses from avernous sinus aneurysms, as treatment is radially different [5, 6]. omparison of the effiay of angiography, CT, and MR in the evaluation of parasellar lesions is the subjet of this report. Materials and Methods This artile appears in the September/Otober 1988 issue of JNR and the November 1988 issue of JR. Reeived September 16, 1987; aepted after revision February 19, Department of Radiology, Presbyterian-University Hospital and University of Pittsburgh Shool of Mediine, DeSoto at O'Hara Sts., Pittsburgh, P ddress reprint requests to W. L. Hirsh, Jr. 2 Department of Neurosurgery, Presbyterian University Hospital and University of Pittsburgh Shool of Mediine, Pittsburgh, P JNR 9: , September/Otober /88/ merian Soiety of Neuroradiology Over a 20-month period, 21 masses that enlarged the avernous sinus were studied with MR and CT; in 18 patients angiography was performed also. Seventeen of the masses were entered in the avernous sinus. Four of the masses (three pituitary adenomas and one hondrosaroma) were entered in the sella and involved the avernous sinus seondarily. There was histologi onfirmation of a neoplasti mass in 15 patients, angiographi and MR onfirmation of four patients, and endorinologi proof of a pituitary adenoma in one patient (Table 1). In one patient the diagnosis of a ompletely thrombosed avernous aneurysm was based on CT and MR riteria alone. This presumed aneurysm ould not be seen angiographially beause of thrombosis of the aneurysm and the ipsilateral arotid artery. ll imaging studies were done within 1 week of one another in 16 patients and within 1 month of one another in four patients. In one patient with a plexiform neurofibroma, CT and MR studies were performed 6 months apart. CT was performed on a GE 9800 sanner' in 19 patients and on a Piker 1200 sanner t in two patients. Contrast material was administered to 20 patients by IV drip infusion. One patient did not reeive ontrast material owing to allergy. Coronal and axial CT sans were obtained in 13 patients. xial images only were obtained in eight patients. The avernous, General Eletri Medial Systems, Milwaukee, WI. t Piker International, Cleveland, OH.

2 908 HIRSCH ET L. JNR:9, September/Otober 1988 TLE 1: Summary of Patients with Parasellar Masses and Method of Diagnosis Case No. ge Gender Diagnosis Confirmation 1 63 M Meningioma Histology 2 63 F Meningioma Histology 3 52 M Meningioma Histology 4 41 F Reurrent meningioma Histology 5 56 F Reurrent meningioma Histology 6 63 M Reurrent meningioma Histology 7 36 F Reurrent meningioma Histology 8 49 M Pituitary adenoma Histology 9 72 F Pituitary adenoma Histology M Pituitary adenoma Elevated prolatin M Nerve sheath tumor Histology F Fifth nerve sheath tumor Histology M denoysti arinoma Histology M Chondrosaroma Histology 15 3 M Plexiform neurofibroma Histology M Metastati renal ell arinoma Histology F Cavernous arotid aneurysm MR, angiography M Cavernous arotid aneurysm MR, angiography F Cavernous arotid aneurysm MR, angiography F Thrombosed aneurysm MR F ilateral avernous arotid aneurysms MR, angiography Fig. 1.-Case 17: Giant aneurysm in 30-year-old woman with double vision., Coronal ontrast-enhaned CT san shows uniformly enhaning smooth mass with assoiated remodeling of lateral wall of sphenoid sinus., T1-weighted oronal MR image defines mass as uniform region of almost absent signal, onsistent with flowing blood. C, Lateral lett internal arotid angiogram shows large avernous arotid aneurysm. sinus was sanned with 3-mm uts in 11 patients and 5-mm uts in 1 0 patients. MR was performed on a GE superonduting unit operating at 1.5 T. Coronal spin-eho T1-weighted images, /20 (TRJTE), were obtained in all patients with a 128 x 256 or aquisition matrix, a 12- to 20-m field of view, two to six exitations, a 3- to 5- mm slie thikness, and a 1- to 2.5-mm interslie skip fator. Long TR intermediate or T2-weighted images, 2500/25,50,75,100, were obtained in the oronal plane in 12 patients and in the axial plane in nine patients with a 5-mm slie thikness, 1- to 2.5-mm skip fator, 128 x 256 aquisition matrix, and 16- to 20-m field of view. lowresolution T1-weighted sagittal image was usually obtained as a sout view. ngiography was performed in 13 of the 16 patients with neoplasti masses, usually as part of a balloon test olusion of the ipsilateral internal arotid artery [4, 6]. ngiography was performed in all patients with aneurysms. Results CT, MR, and angiography were eah evaluated for their ability to distinguish aneurysms from other masses and for their ability to define the relationship of nonaneurysmal masses to surrounding strutures. neurysm vs Neop/asti Mass Six of 21 expansions of the avernous sinus were aused by aneurysms of the parasellar segment of the arotid artery.

3 JNR :9, September/Otober 1988 IMGING THE ENLRGED CVERNOUS SINUS 909 Four of these aneurysms showed uniform enhanement on CT and were indistinguishable from a neoplasm suh as a meningioma or nerve sheath tumor (Figs. 1) [7, 8]. On MR, three of these four appeared as signal voids, often with assoiated phase-enoding artifats and low-level internal ehoes probably related to turbulent flow within the aneurysm lumen (Fig. 1 ) [7, 9]. In one patient with the same CT appearane, the aneurysm lumen was of intermediate signal intensity on T1-weighted images and had mixed high- and low-intensity T2 signal (Fig. 2). t angiography this aneurysm demonstrated extremely slow flow within its lumen, whih may aount for the higher-level internal ehoes. One giant avernous aneurysm had rim alifiation and entral "target" enhanement on CT (Fig. 3). MR showed the entral enhaning area as a signal void assoiated with phase-enoding artifats, suggesting luminal flow. The surrounding tissue had heterogeneous signal on both T1- and T2-weighted images, representing thrombus within the aneurysm lumen (Figs. 3 and 3C). ngiography was somewhat misleading in this ase beause it showed fusiform dilatation of the petrous and parasellar arotid but did not demonstrate the large amount of luminal thrombus (Fig. 3D). The remaining aneurysm appeared as a ring-enhaning mass on CT and was interpreted as nonvisualization of the ipsilateral internal arotid on ere- bral angiography (Fig. 4). MR showed intense signal within the mass and adjaent avernous arotid on all pulsing sequenes. Neop/asti Masses: Relationships to Surrounding Strutures 8 Fig. 2.-Case 19: Giant avernous arotid aneurysm in 80-year-old woman with gradually progressive ophthalmoplegia., CT appearane of smooth, uniformly enhaning left paraseliar mass is nonspeifi., Mass is haraterized by dereased signal intensity on T1-weighted image (arrowheads). Signal within mass is greater than flow void manifested by adjaent left middle erebral artery (arrow). Left 1 segment indents undersurfae of brain, giving lateral aspet of suprasellar istern a rounded onfiguration. This should not be onfused with aneurysm (arrowheads). Though the image is suggestive, it is diffiult to make a definitive diagnosis. C, T2-weighted oronal image shows inhomogeneous areas of high and low signal intensity most likely related to flow-rate variation within aneurysm (arrowheads). D, Left arotid angiogram shows avernous arotid aneurysm. E, neurysm retains ontrast material (arrow) 0 well into venous phase, indiating slow flow. In the 16 neoplasti masses, eah imaging method was evaluated for its ability to depit the relationships of the mass to the arotid arteries, ranial nerves III-VI, the opti hiasm/ infundibulum, the sphenoid sinus, and the bone of the skull base. Carotid artery.-ngiography, CT, and MR were ompared for their ability to demonstrate arotid displaement by tumor (Fig. 5). MR of a parasellar mass allows for simultaneous visualization of the mass and both arotid arteries. This failitates determination of arterial displaement or enasement by tumor. Normal variation, anatomi overlap, and lak of simultaneous bilateral opaifiation makes visualization of subtle avernous arotid displaement diffiult on angiography (Fig. 5). lthough angiography an demonstrate neoplasti narrowing ourring with advaned arotid enasement (Fig. 6) [10], enasement not resulting in narrowing was not apparent on angiography but was easily seen with MR (Fig. 7). CT was ineffetive in demonstrating displaement or en E

4 910 HIRSCH ET L. JNR :9. September/Otober 1988 D Fig. 3.-Case 18: Giant parasellar aneurysm in 31-year-old man with double vision. neurysm was treated by transatheter balloon olusion of right internal arotid., Coronal CT san shows large right parasellar mass with rim alifiation and entral area of enhanement (arrow)., Coronal T1-weighted MR image shows signal void within patent lumen of aneurysm (arrow). Lumen is surrounded by thrombus, whih has mottled signal of intermediate intensity. C, Coronal T2-weighted image at same level shows mixed signal within thrombus. Low signal peripherally, whih is more prominent than on the T1-weighted image, may reflet T2 shortening from hemosiderin deposition within peripheral aspet of thrombus (arrow). D, nteroposterior angiogram shows fusiform aneurysm of petrous portion of right internal arotid artery. E, Coronal T1-weighted MR image 1 month after right internal arotid olusion. Thrombus now has muh higher signal than on preembolization study and is similar in intensity to more reent thrombus in arotid lumen (arrow). asement of the arotid beause of onomitant enhanement of the arotid. the avernous sinus. and the mass itself (Fig. 5). Cranial nerves.-in the 16 neoplasms studied, the ipsilateral intraavernous segments of ranial nerves III, IV, and VI were not identified in any ase by MR or CT. In ontrast, Mekel ave, whih ontains V 1 and sometimes V 2, was routinely demonstrated by both methods. This CSF-filled refletion of dura was routinely seen on enhaned CT as a low density within the posterior inferior aspet of the enhaned avernous sinus (Fig. 8). On T1-weighted images. Mekel ave appeared as a foal area of low signal intensity (Fig. 8). and on T2-weighted images it had high signal intensity similar to CSF (Fig. 8G). Ipsilateral to the mass, Mekel ave was ompletely effaed in 10 patients, partially ompressed in four patients, and normal in two patients. Contralateral to the mass, Mekel ave was visualized and normal in 15 patients, but partially effaed by a large hondrosaroma (that rossed the midline) in one patient. Idential findings were noted on enhaned CT sanning in 13 patients. In three ases, neither ipsilateral nor ontralateral Mekel ave ould be demonstrated by CT despite 5-mm uts through the area. Dural refletions of the avernous sinus.-on CT, the dural refletion forming the lateral wall of the avernous sinus was identified as a thin rim of enhanement surrounding the tumor [10]. This was seen in eight of 16 patients. On MR, the lateral dural refletion appeared as a thin rim of low signal adjaent to the mass on T1-weighted images (Fig. 8). This rim was visible in all patients, but was inomplete in four: three previously operated meningiomas and one large pituitary adenoma that invaded the temporal lobe. The lateral wall of the avernous sinus was onvex laterally (bulging) in all of the avernous sinus neoplasms studied. Early involvement of the avernous sinus by neoplasm without bulging in the lateral wall was not observed. In ontrast to the exellent demonstration of the lateral wall of the avernous sinus, the medial wall bordering the pituitary fossa was not seen in any patient. Opti hiasm/infundibulum.- The opti hiasm and infundibulum were demonstrated more reliably on MR than on CT. With MR the hiasm was identified in 16 of 16 patients with parasellar neoplasms, whereas CT delineated the hiasm in 13 of 16 patients. The infundibulum was identified in all patients with both MR and CT. eause of inreased ontrast with MR, anatomi definition of both the hiasm and infundibulum was superior to CT [11]. Sphenoid sinus and skull base.-the one area where CT

5 JNR :9, September/Otober 1988 IMGING THE ENLRGED CVERNOUS SINUS 911 Fig. 4.-Case 20: Thrombosed aneurysm in 49-year-old woman with 2-week history of periorbital pain and left sixth nerve palsy., xial ontrast-enhaned CT san delineates ring-enhaning left parasellar mass., Coronal T1-weighted image illustrates largely hyperintense mass onsistent with subaute thrombus. Note thrombosed portion of adjaent left avernous internal arotid artery (arrowhead). C, xial T2-weighted image. Mass remains primarily hyperintense, with well-defined internal ring of dereased signal intensity, illustrating laminar omposition (arrows). D, Left vertebral angiogram shows filling of left middle erebral artery and left internal arotid artery (supralinoid portion). Injetion of both ommon arotid arteries also failed to show aneurysm. D Fig. S.-Case 2: Left parasellar meningioma in 63-year-old woman with 1Y2-year history of left faial pain., Coronal CT san shows a uniformly enhaning left parasellar mass. Left avernous arotid artery annot be identified. Inidently noted is alifiation in ontralateral right avernous arotid artery (arrow)., Lateral left arotid angiogram defines avernous arotid. There is subtle superior displaement of avernous segment and a question of narrowing of preavernous segment (arrow). C, Coronal T2-weighted MR image learly shows that left avernous arotid artery (arrow) is superiorly displaed by isointense meningioma.

6 912 HIRSCH ET L. JNR:9, September/Otober 1988 Fig. 6.-Case 7: 36-year-old woman with reurrent left avernous sinus meningioma., Lateral left arotid angiogram shows narrowing of avernous and preavernous internal arotid artery seondary to enasement (ar rows)., Slightly hypo intense meningioma on n weighted image enases avernous arotid, whih is seen as small irular flow void (arrow). Fig. 7.-Case 14: 25-year-old man with reurrent hondrosaroma., nteroposterior left arotid angiogram shows unoiling of arotid siphon without evidene of luminal narrowing., T2-weighted oronal image shows avernous arotid (arrow) almost totally engulfed by tumor, whih has very intense signal harateristis. Fig..-Case 11 : Large fifth nerve sheath tumor ("trigeminal neuroma" ) in 31-year-old man with deteriorating mental status and hydroephalus., Coronal ontrast-enhaned CT san shows large, uniformly enhaning mass in right avernous sinus. Mekel ave is ompletely effaed on right and is normal on left (arrow)., T1-weighted oronal image shows mass to be slightly hypointense relative to brain. Low-signal rim (arrowheads) may represent dural refletion forming lateral margin of avernous sinus. Mekel ave is obliterated on right by tumor. Note normal appearane of Mekel ave on left (arrow). C, xial T2-weighted image. Mass is markedly hyperintense relative to brain. Note intense signal in normal left Mekel ave (arrow). This ase illustrates that on T2-weighted images a small fifth nerve sheath tumor may be missed beause it an have signal harateristis similar to CSF, whih normally oupies Mekel ave.

7 JNR :9, September/Otober 1988 IMGING THE ENLRGED CVERNOUS SINUS 913 was learly superior to MR was in the evaluation of bone hanges adjaent to avernous sinus masses. In 16 patients with neoplasti masses, MR showed gross invasion of the sphenoid sinus in four, remodeling of the sellar floor in three, a hypoplasti sphenoid sinus in one, and no abnormality in eight. CT findings were idential to those of MR exept in one pituitary adenoma with erosion of the anterior sellar floor, a potentially helpful finding not visible on MR (Fig. 9). Hyperostosis was deteted by CT in five of seven avernous meningiomas. Corresponding MR sans were reviewed to look for bone hanges onsistent with hyperostosis (thikening of ontour, indistintness of ortial margins, inreased marrow signal) [12]. Retrospetively, MR demonstrated bone hanges in all five of these patients (Fig. 10). Signal Charateristis of Parase//ar Masses Of the seven meningiomas, T1-weighted images showed six to be isointense relative to brain, and one was minimally hypointense. On T2-weighted images, six meningiomas were isointense and one was hyperintense. ll three pituitary maroadenomas were isointense relative to brain on T1- and T2- weighted images. Neoplasms other than meningiomas and pituitary adenomas were hypointense on T1- and hyperintense on T2-weighted images [13]. Disussion Reent advanes in tehnique allow suessful surgial removal of masses involving the avernous sinus, often without impairment of ranial nerve funtion and with preservation of pateny of the arotid artery. Prior to this extensive surgery, imaging is used to exlude aneurysm and to determine the relationship of parasellar neoplasms to the avernous arotid; the opti hiasm; ranial nerves III, IV, V, and VI ; the pituitary gland; and the bone surrounding the parasellar region [3, 4]. MR is superior to drip-infusion CT in differentiating giant avernous aneurysms from neoplasms (Figs. 1 and 2). However, the diagnosti auray of CT is dramatially improved Fig. 9.-Case 10: Pituitary adenoma in 48-year-old man with elevated prolatin levels., Contrast-enhaned 1.S-mm-thik oronal CT san shows foal remodeling of anterior aspet of sella aused by pituitary adenoma., one algorithm delineates thinning of wall of sphenoid adjaent to adenoma (arrowhead). C, Coronal T1-weighted image through same region shows adenoma, but adjaent bone annot be distinguished from air in sphenoid sinus. Fig. 10.-Case 6: Reurrent meningioma in 63-year-old man., xial CT san with bone algorithm shows hyperostosis of left sphenoid and temporal bones (arrowhead)., Comparable axial T1-weighted MR image. Hyperostoti bone of floor of left temporal fossa (arrowhead) is visibly thikened and has higher signal than normal bone. CT and MR images were both obtained at level of internal auditory anals.

8 914 HIRSCH ET L. JNR:9, September/Otober 1988 by using dynami sanning and bolus injetion of ontrast material [14]. With this tehnique, CT and MR probably are of nearly equal effiay in differentiating neoplasti and aneurysmal parasellar masses. MR and dynami ontrast CT have advantages over angiography in the evaluation of some parasellar aneurysms, speifially those that are partially or ompletely thrombosed. In partially thrombosed aneurysms, angiography underestimates aneurysm size by showing only the lumen, while MR and CT demonstrate the lumen and the mural lot (Fig. 3). Completely thrombosed aneurysms, whih appear as a nonspeifi blush on angiography and as a ringenhaning mass on CT, are best haraterized on MR (Fig. 4). Despite the suess of MR in the evaluation of giant aneurysms, several pitfalls in diagnosis remain. Small «1 m) avernous aneurysms an be diffiult to distinguish from normal tortuosity of the avernous arotid. Flow-rate variation in large patent aneurysms results in a wide spetrum of signal harateristis within the lumen. These range from a signal void when flow is rapid (Fig. 1 ) to an isointense or even hyperintense signal (Figs. 2 and 2C) when flow within the aneurysm lumen is slow or turbulent. In ambiguous ases dynami ontrast bolus CT or angiography may be required for diagnosis. Low-flip-angle gradient-realled eho sequenes also may be a reliable method of differentiating a solid mass from slow or turbulent flow within giant aneurysms, but this will have to be substantiated. nother potential problem is that the signal of lot within a ompletely or partially thrombosed aneurysm may vary onsiderably depending on its age and the presene of an adjaent patent vasular lumen (Figs. 3, 3C, and 3E). eause of this variation, it is oneivable that the signal harateristis of lot may be similar to those of a neoplasti mass. Hemorrhagi neoplasms might also be onfused with aneurysm [7]. In the evaluation of avernous sinus neoplasms, MR is generally more informative than CT, partiularly in establishing the relationship of the neoplasm to surrounding strutures. T1-weighted oronal images were the most valuable imaging sequene. The relationships of the parasellar masses to the arotid, pituitary fossa, suprasellar istern, medial temporal lobe, sphenoid sinus, and Mekel ave were all well demonstrated. Cavernous sinus masses may displae ranial nerves within the avernous sinus in any diretion, and preoperative visualization is useful in surgial planning. Cranial nerves III, IV, V 1, and sometimes V 2 are intimately related to the lateral wall of the avernous sinus, and ranial nerve VI runs within the sinus itself [2]. The intraavernous segments of ranial nerves III, IV, and VI were not visualized ipsilateral to the mass with either CT or MR in any patient in our series, possibly beause of effaement by the adjaent mass. These nerves often are so attenuated that they are not visible at surgery, and an only be demonstrated intraoperatively by diret eletrial stimulation and eletromyographi monitoring of the extraoular musles [3]. In the normal avernous sinus, visualization of ranial nerves III, IV, and VI has been reported on both MR and CT [15]. Our preliminary experiene with gadolinium-enhaned oronal T1-weighted images suggests that they will be superior to oronal CT and unenhaned MR in the definition of these ranial nerves in normal subjets. It may remain diffiult, however, to demonstrate these strutures in the presene of a large avernous sinus mass. The T2 signal harateristis of parasellar neoplasms were useful in limiting the differential diagnosis. In this small series six of seven parasellar meningiomas and the three pituitary maroadenomas involving the avernous sinus were hypointense or isointense on T1- and T2-weighted sequenes (relative to white matter). Similar findings have been observed by others [12, 13]. The six parasellar neoplasms with other histologies all had low T1 and high T2 signal intensities. Signal harateristis, however, are of limited speifiity. Some meningiomas have inreased T2 signal intensity, and these will be diffiult to differentiate from other parasellar masses on the basis of signal harateristis alone [12]. Pituitary maroadenomas also an have variable signal harateristis, partiularly if they are avitated [16, 17]. limitation of both CT and MR is the reognition of very small parasellar neoplasms that do not distort the ontour of the avernous sinus but are still able to produe symptoms, usually a ranial nerve palsy. In partiular, small isointense meningiomas might be overlooked by MR. In suh ases CT may be helpful beause of its superb sensitivity to alifiation and hyperostosis. While MR did show evidene of hyperostosis in five of seven meningiomas, this analysis was retrospetive. The ability of MR to prospetively detet hyperostosis without benefit of omparison CT remains to be established. In patients with signs of a parasellar lesion (suh as unilateral ophthalmoplegia, sensory defiits in the V 1 and V 2 distribution, and retroorbital pain) [18], both enhaned CT and MR direted at examining the parasellar region (oronal plane, 3- to 5-mm uts through area) are apable of deteting most parasellar masses. ngiography does little in narrowing the differential diagnosis of neoplasms, and aneurysm an usually be diagnosed noninvasively by using MR or dynami bolusontrast CT [4, 5, 7]. However, when surgial intervention is onsidered, angiography still provides anatomi information not available with other methods, suh as tumor vasularity [10] and the haraterization of the nek of aneurysms. We also advoate transatheter balloon test olusion of the ipsilateral arotid artery prior to avernous sinus surgery, believing that test olusion is helpful in prediting whih patients an tolerate sarifie of the arotid artery, whether it is intentional or is a ompliation of avernous sinus surgery [4]. The usefulness of this later proedure is urrently being reviewed. Interventional neuroradiology also plays an inreasing role in treatment. Olusion of the lumen or parent vessel with detahable balloons has beome the treatment of hoie for giant parasellar aneurysms in some enters [5, 19]. In summary, when available, MR should be the initial diagnosti method in the evaluation of patients with suspeted parasellar masses. The advantages of MR are first in deiding whether the lesion is an aneurysm or neoplasm and, seond, in defining the regional anatomi relationships more aurately than an be aomplished with CT. ngiography and CT will ontinue to have important supplementary roles in the evaluation of these masses, partiularly when surgial intervention is planned.

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