Lipoma in the Cerebellopontine Angle -Case Report

Shigeru NISHIZAWA, Tetsuo YOKOYAMA, Seiji OHTA, Hiroshi RYU, Toshiaki NINCHOJI, Ichiro SHIMOYAMA, Seiji YAMAMOTO, Yasushi SUGIURA, Kenichi UEMURA and Michihiko NOZUE*

Departments of Neurosurgery and *Otorhinolaryngology, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka

Abstract

The authors report a case of a cerebellopontine (CP) angle lipoma with a very unusual histological ap pearance. The 38-year-old male patient suffered vertigo, left tinnitus, and left hearing disturbance. Computed tomography and magnetic resonance imaging showed a nonenhanced low-density area and a high-intensity region in the left CP angle, respectively. The tumor, which was only partially removed because of its tight adhesion to the VIIIth nerve and brainstem, consisted of mature lipocytes and contained a piece of cartilage, which is highly unusual.

Key words: cerebellopontine angle tumor, lipoma, hamartoma, auditory brainstem response

Introduction mus to the right and made a diagnosis of sudden deafness. He was referred to our institution for Intracranial lipomas are very rare and are usually further evaluation on March 9, 1989. situated in the corpus callosum.3,9,") Other locations Neurological examination disclosed a 30-40 deci include the chiasmatic, ambient, quadrigeminal, and bel (dB) neural hearing loss (Fig. 1), and a markedly interpeduncular cisterns, Sylvian fissures, choroid diminished caloric response on the left side. Audito plexus, and tela choroidea of the third and fourth ry brainstem responses (ABR) following the left ear ventricles. 9,") Lipomas of the cerebellopontine (CP) stimulation showed poor discrimination of the third, angle are extremely rare, 1-3,6-8,11)and their patho fourth, and fifth waves, as compared to those logical features have not been described in detail. following the right ear stimulation the right, al We describe a case involving a CP angle lipoma though respective peak latencies appeared the same with an unusual histological appearance and review on both sides (Fig. 2). Computed tomographic (CT) the literature. scans revealed a small low-density lesion in the left CP angle, which was not enhanced by contrast Case Report medium (Fig. 3). The density was 70 to 80 Hounsfield units in a scale of 1000. Both T, and A 38-year-old male who had been healthy until proton density-weighted magnetic resonance (MR) December 14, 1988, experienced sudden onset of images clearly showed a high-intensity lesion in the intermittent vertigo accompanied by nausea and left CP angle (Fig. 4). Moreover, a T,-weighted MR vomiting, and was admitted to a local hospital. image demonstrated a low-intensity area within the Although these symptoms disappeared after several lesion. However, vertebral angiograms showed no days, he developed left hearing disturbance and low abnormalities. pitched, continuous tinnitus. An otolaryngologist Lipoma of the left CP angle was the preoperative noted mild hearing disturbance and rotatory nystag diagnosis, and he underwent surgery on May 15, 1989 under intraoperative ABR monitoring. A Received October 9, 1989; Accepted January 11, glossy, yellowish tumor was discovered in the left CP 1990 angle, completely obscuring the VIIIth cranial nerve Fig. 3 Preoperative precontrast CT scans, disclosing a low-density area in the left CP angle (left). The lesion is not enhanced by contrast medium (right). The density of the lesion is -70 to -80 Hounsfield units. Fig. 1 Preoperative pure-tone audiogram, showing a 30-40 decibel (dB) neural hearing loss on the left side. The hearing loss at 4000 Hz is due to long-term exposure to loud noise. C : right the tumor from the VIIIth nerve without causing air conduction, x : left air conduction, -1 : left damage became so difficult that we finally resorted bone conduction. to merely debulking it. The postoperative course was uneventful, and no cranial nerve disturbance was encountered. His audi tory acuity and ABR recordings were unchanged. The continuous tinnitus disappeared for 1 month, probably because of minor injury to the VIIIth nerve during surgery. Histological examination showed the tumor to con sist of mature lipocytes and connective tissue. The hard fragment within the tumor exhibited the typical structure of mature cartilage (Fig. 6), and this was identified as the source of the low-intensity intra tumoral area observed on T1-weighted MR imaging.

Discussion

Fig. 2 Preoperative auditory brainstem responses to Lipomas in the CP angle are extremely rare; to our ear stimulation show poorer discrimination of knowledge, only 23 cases of CP angle lipoma have the third, fourth, and fifth waves on the left been reported in the world literature. 1-4,6-8,10,12-17,19,22) than on the right, although the latencies are not Generally, surgery is not indicated, for the following prolonged. reasons: 1) Although a lipoma in the corpus callosum may be accompanied by neurological signs and symptoms, such as seizures, it is generally at its entrance to the brainstem. The Vth nerve and thought that these are caused not by the tumor itself the complex of IXth, Xth, and Xlth nerves were but by the associated dysgenesis of the brain. 2) slightly compressed by the tumor. The facial nerve Lipomas in other locations do not produce neuro was not exposed. The tumor was highly vascular, logical symptoms and are usually found incidentally, and was removed piecemeal. Within the tumor, a either at autopsy or on CT scans. Lipomas in the small, white, hard fragment resembling bone was CP angle are entirely different from those at other found (Fig. 5). During removal of the tumor, ABR sites. These lesions are usually symptomatic and the monitoring disclosed prolonged latencies for each symptoms are derived from the tumor itself, which wave, and about 30 minutes later it became more affects the cranial nerves, brainstem, and/or cere difficult to discriminate the fifth wave. Dissecting bellum. Among the 24 reported cases (including Fig. 4 Magnetic resonance T,-weighted axial (left) and sagittal (center) images and proton density weighted image (right). On all images, the lesion in the left CP angle shows high signal intensity, indicating fatty tissue. Also, a small low-intensity area within the tumor is observed on the T, weighted image (arrowhead).

Fig. 5 Intraoperative photographs showing the glossy, yellowish tumor in the left CP angle. left: The tumor completely ensheaths the proximal portion of the VIIIth nerve (arrowhead). right: A small, white fragment (arrowheads) is observed within the tumor.

Fig. 6 Photomicrographs of tumor specimens, revealing mature lipocytes and connective tissue (left) and mature cartilage (right). HE stain, x 200. ours), 18 entailed some symptoms due to involve weighted MR imaging. 5'12'14'17) Common CP angle ment of the VIIIth nerve. Unilateral hearing distur tumors, i.e., acoustic neurinomas and epidermoid or bance was noted in 14, tinnitus in 11, and vertigo teratoid tumors, also contain fatty components.23' in nine cases. Other symptoms included cerebellar Correct diagnosis of such lesions requires surgical ex ataxia, decreased facial sensation, trigeminal neu ploration; 18 of the 24 reported patients 1-3,6,7,12-17,19,22) ralgia, and hemifacial spasm. underwent surgery. Neurological and radiological examinations do Totally removing a CP angle lipoma without not always differentiate lipomas from other lesions in sacrificing the VIIIth nerve is difficult because of the the CP angle. The symptoms mentioned above are tumor's tight adhesion to the nerve. Fortunately, also very common with other CP angle lesions. In total removal of these tumors is unnecessary, since tracranial fatty tissue is easily detected radiological neither malignant change nor rapid growth of ly, appearing as low density on CT'-',',', 12,14,16,17,19,23) lipomas in the CP angle has ever been reported.',"' and as high intensity on T1-, proton density-, and T2 The purposes of surgery, then, are to make the cor

Table 1 Summary of reported cases of CP angle lipoma

NR: not reported. rect diagnosis and to decompress the affected nerves. 4) Faerber EN, Wolpert SM: The value of computed ABR monitoring is most helpful during surgery, tomography in the diagnosis of intracranial particularly for preservation of the VIIIth nerve.") lipomata. J Comput Assist Tomogr 2: 297-299, 1978 CP angle lipomas are unilateral, arising primarily 5) Friedman RB, Segal R, Latchaw RE: Computerized on the left side (Table 1). The patients are tomographic and magnetic resonance imaging of in tracranial lipoma. Case report. J Neurosurg 65: 407 predominantly male (16 vs. six females among those 410, 1986 - reported; in two cases the sex was not mentioned). 6) Fukui M, Tanaka A, Kitamura K, Okudera T: The developmental origin of intracranial lipoma is Lipoma of the cerebellopontine angle. Case report. J controversial. Schmid"' summarized the prevailing Neurosurg 46: 544-547, 1977 hypotheses as follows: 1) displacement of embryonic 7) Graves VB, Schemm GW: Clinical characteristics presumptive mesenchymal cells; 2) hyperplasia of and CT findings in lipoma in the cerebellopontine normal fat cells within the pia; 3) lipomatous angle. Case report. J Neurosurg 57: 839-841, 1982 metaplasia of connective tissue; and 4) lipomatous 8) lanovici N, Dimitriv-Pausesti M, Costschescu G: metaplasia of pial cells. In any event, lipocytes are Lipoma of the pontocerebellar angle. Rev Med Intern mesenchymal cells that originate from the meso [Neurol Psihiatr] 21: 271-274, 1976 derm. 9) Kazner E, Stochdorph 0, Wende S, Grumme T: In As Budaka" suggested, intracranial lipoma has a tracranial lipoma. Diagnostic and therapeutic con siderations. J Neurosurg 52: 234-245, 1980 hamartomatous character. He noted that it should 10) Klob J: Zur Pathologie der Fettsgeschwulste. be classified as a true hamartoma and termed "lipomatous hamartoma" rather than "lipoma Gesellsch Arzte Wien, pp 673-675, 1859, cited in 2) ." 11) Leibrock LG, Deans WR, Bloch S, Schuman RM, Although intracranial lipomas sometimes contain Skultety FM: Cerebellopontine angle lipoma: A such metaplastic elements as bone, cartilage, and eview. Neurosurgery 12: 697-699, 1983 r even muscle fibers," such components are rarely ob 12) Levin JM, Lee JF: Hemifacial spasm due to cere served in lipomas in the CP angle. Among the 23 bellopontine angle lipoma: Case report. Neurology previously reported cases, bony elements 7) and car 37: 337-339, 1987 tilage') were found in only one case each. Our case 13) Mattern WG, Blattner RE, Werth J, Schuman R, was highly unusual in that the tumor contained Bloch S, Leibrock LG: Eighth nerve lipoma. Case report. J Neurosurg 53: 397-400, 1980 mature cartilage. 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