ELSEVIER Clinical Neurology and Neurosurgery 98 (1996) 27-31

Clinical Neurology and Neurosurgery

Case report

Lipomas of the frontal lobe

Hikaru Sasaki*, Kazunari Yoshida, Hirooki Wakamoto, Mitsuhiro Otani, Shigeo Toya

Department of Neurosurgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160 Japan

Received 1 May 1995; revised 18 July 1995; accepted 24 August 1995

Abstract

An extremely rare case of lipomas on the cerebral surface in a 65-year-old female is reported. The tumors were located both in an unusual fissure of the right frontal convexity and under the right frontal lobe associated with and surrounded by areas of focal cortical dysplasia. Angiograms revealed dilated branches of the right anterior cerebral artery associated with angiomatous tumor blushes. The etiology of the combination of the lipomas and the anomalies, and the angiographic features, are briefly discussed.

Keywords." Intracranial lipoma; Cerebral surface; Frontal lobe; Abnormal fissure; Hypervascularity

1. Introduction

Intracranial lipomas are rare lesions, which represent 0.1-1.7% of all intracranial tumors [14] and are found in less than 0.1% of all computed tomographic (CT) examinations [2,3]. They preferentially occur near the midline, most frequently in the pericallosal cistern, and are often associated with various neurologic and sys- temic anomalies. Since the advent of CT scanning and magnetic resonance (MR) imaging, unexpected findings of intracranial lipomas have increased [5-8]. However, lipomas on the cerebral surface, exclusive of the cases in the sylvian fissure, are extremely rare [9-12]. In this paper, we present a rare case of intracranial lipomas of the frontal lobe associated with focal migrational defects of the surrounding cerebral cortex.

2. Case report

A 65-year-old right-handed woman consulted a nearby hospital in July, 1993, with a 3-month history of right frontal headache. MR imaging of the brain was performed and mass lesions in the right frontal lobe were

*Corresponding author, Fax: (+81) 3-3354-8053.

0303-8467/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 0303-8467(95)00073-9

detected. She was referred to our hospital for further examination and admitted on September 8, 1993. She had undergone a resection of the upper lobe of the right lung in 1951, for lung tuberculosis, a hysterectomy in 1969, for myoma of the uterus, and a subtotal gastrec- tomy in 1984, for gastric cancer. There was no history of seizures in her life and her familial history was unre- markable.

On admission, there was no particular finding other than operative scars on physical examination. Neurol- ogic examination was normal, and routine laboratory studies were negative. Her headache was due to muscular contraction and was not related to the mass lesions de- tected. Plain skull x-ray films were unremarkable. CT scans disclosed extremely low density areas in the right frontal region and postcontrast scans showed irregularly enhanced areas within the lesions (Fig. 1). On T1- weighted MR images, the lesions were hyperintense, and, by coronal sections, clearly shown to be located both under the right frontal lobe and in an unusual fissure of the right frontal convexity (Fig. 2A). They were slightly enhanced in the periphery by Gd-DTPA administration. T2-weighted images revealed the lesions as mildly hyper- intense areas, and showed clearly abnormal infoldings of gray matter associated with the respective lesions (Fig. 2B). Surface MR images vividly demonstrated the abnormalities of gyration and sulcation around the le-

28 H. Sasaki et al. / Clinical Neurology and Neurosurge O, 98 (1996) 27 31

very easily by piecemeal resection. Because histological examination by frozen section revealed mature adipose tissue, we diagnosed the tumors to be lipomas, and the operation was closed at that time. Permanent section also showed the typical appearance of adipose tissue indicative of lipoma.

The patient 's postoperative course was uneventful. She was discharged home with no neurological deficit.

3. Discussion

Intracranial l ipomas have a predilection for certain sites and are commonly seen in the pericallosal, quad- rigeminal/supracerebellar (so called 'dorsal mesenceph-

Fig. 1. Postcontrast CT scan showing an extremely low density area with irregular enhancement in the right frontal region.

sions (Fig. 3). On fat saturation images, the hyperinten- sity of the lesions on T 1-weighted M R images was de- creased and they could be barely detected. Right carotid angiograms revealed dilatation and tortuosity of the right anterior cerebral artery and its branches, an or- bitofrontal artery and an anterior internal frontal artery, associated with the angiomatous capillary blushes con- sistent with the tumor locations of MR images (Fig. 4A). On the venous phase, two dilated cortical veins along the lesions were shown (Fig. 4B). Based on these radiological findings, we considered the lesions to be tumors with hypervascularity, which were abundant in fatty compo- nent, associated with disorganization of the surrounding cortex. Teratoma, tuberculoma, lipoma, dermoid cyst, and other tumors associated with abnormal hypervascu- larity or possibly combined with vascular malformative lesions were taken into consideration for differential di- agnoses.

The patient underwent a right frontal craniotomy. A large abnormal fissure transversing the frontal lobe was viewed, and yellowish tumors were found in the abnor- mal fissure and under the frontal lobe (Fig. 5). The tu- mors were coursed through by the branches of the ante- rior cerebral artery and dilated bridging veins respec- tively. They contained numerous blood vessels and bled

Fig. 2. A: Coronal Tl-weighted MR image demonstrating the masses as markedly hyperintense areas. Two lesions located both under the right frontal lobe with associated thickening of the cortex and in the abnormal fissure of the right frontal convexity are visible. B: Sagittal T2-weighted MR image showing mildly hyperintense masses (arrow- heads) and deep infoldings of thickened cortex in association with them.

IL Sasaki et al. /Clinical Neurology and Neurosurgery 98 (1996) 27-31 29

by Britt et al. [11] is similar to the present case as regards tumor location related to the surrounding cerebral cor- tex. The authors described a 29-year-old woman with a history of seizures who had had a lipoma in an abnormal cortical invagination of the left frontal convexity and had undergone surgical treatment successfully. Three other reports described cases of lipoma over the cerebral sur- face. Two were cases found at autopsy [9,10], and Fujii et al. [12] reported a case of lipoma over the parasagittal centroparietal lobes diagnosed by MR images in a 4- year-old boy with generalized tonic seizures. In this paper, an exceptional case is presented including two lipomas arising on the cerebral surface: one was located in the unusual fissure of the right frontal convexity, and the other on the inferior surface of the right frontal lobe.

Fig. 3. Surface MR image demonstrating the unusual large fissure of the right frontal lobe (double arrow) and the abnormally smooth corti- cal surfaces adjacent to it. Usual right superior and inferior frontal sulci are absent.

alic lipoma'), and interpeduncular (often related to the tuber cinereum and mammillary bodies) regions [3,5,7]. Other less frequent locations previously reported are the chiasmatic cistern [3,13], anterior interhemispheric fis- sure [5,14], lamina terminalis cistern [5], velum interpos- itum cistern [3,5], cerebellopontine angle [5,15], internal auditory canal [5], sylvian fissure [5,6,14,16,17], and cho- roid plexuses of the lateral and third ventricles [3,8]. Lipomas in the regions of the prepontine cistern [5], cisterna magna [14], and cerebral surface have been re- ported even more rarely, and a few reports of large spinal cord lipoma with extension to the posterior fossa have also appeared [18,19,20]. To date only 4 cases of lipoma have been reported in the literature located on the cere- bral surface, exclusive of the cases in the sylvian fissure (Table 1) [9,10,11,12]. Of these 4 cases, a case reported

Table 1 Cases of intracranial lipomas on the cerebral surface

Author/yr Location Associated anomalies

Scherer 1935 on the parieto-temporo- cortical dysplasia occipital convexity

Demus 1967 on the parasagittal none central lobe

Britt et al. 1993 in a frontal abnormal cortical dysplasia fissure

Fujii et al. 1993 on the parasagittal none centroparietal lobes

Sasaki et al. in a frontal abnormal cortical dysplasia (present case) fissure

under the frontal lobe cortical dysplasia

Fig. 4. Right carotid angiograms, lateral view. A: Arterial phase show- ing dilation and tortuosity of the right anterior cerebral artery and its two branches (arrowheads), and associated abnormal hypervascularity. Neighboring areas show as being rather hypovascular. B: Venous phase showing two tortuous cortical veins draining the areas around the respective masses.

30 H. Sasaki et al./ Clinical Neurology and Neurosurgery 98 (1996) 2~31

Fig. 5. Intraoperative view of the right frontal lobe, showing an abnor- mal fissure (double arrow), two lipomatous tumors (arrowheads), and two bridging veins penetrating them. Polymicrogyric appearance of the surrounding cortex and abnormally developed pial vessels are also seen.

It is generally accepted that intracranial lipomas occur as a result of maldevelopment, and they are often associ- ated with various anomalies of the central nervous sys- tem, such as agenesis/dysgenesis of the corpus callosum [5,13,21], absence of septum pellucidum [5,13,21], cra- nium bifidum [l 3,22,23], spina bifida [21], encephalocele [5], myelomeningocele [21], hypoplasia of vermis [5,13], and malformation of the cortex [16,21,24]. However, the presence of the focal cortical dysplasia as was seen in our case, i.e., the large abnormal fissure which can not usu- ally be recognized and the abnormal cortical surfaces surrounding it, in conjunction with lipoma, is excep- tional, and had never been described before Britt [11]. In our case, the lipoma under the frontal lobe was also associated with abnormal infolding of gray matter. As to the combination of lipoma and anomaly, there have been two ideas: one is that an anomaly arises primarily whether together with a lipoma or not [22,24], and the other is that the occurrence of an anomaly is secondary to the preexistence of a lipoma as frequently considered in cases of agenesis/dysgenesis of the corpus callosum accompanied by pericallosal lipoma [5,21,23]. In our case, the etiology of the combination of the lipomas and the anomalies is not clear. However, considering the ab- normal vascularization around the tumors and the strik- ingly intimate locational relationship between the lipo- mas and the anomalies, there is a possibility that both physical interruption and focal perfusion insufficiency due to the preexistence of the lipomas might contribute to the formation of the focal cortical dysplasias, al- though an another idea also exists, that they might have occurred together resulting from a common cause as a complex malformation [24]. On the pathogenesis of in- tracranial lipomas, the theory that they are a result of abnormal persistence and maldifferentiation of the 'me- ninx primitiva' which as a rule dissolves to form the

primitive subarachnoid space by the end of the eighth gestational week is common in the recent literature [5,13,25]. Meanwhile, with regard to the timing of the formation of the anomalies, most of the cortical dyspla- sias in the form of deep infolding of disorganized cortex, which presumably represent polymicrogyria microscopi- cally [26], are considered to result from injuries in the first half of the second trimester [27]. These concepts support the first of the two ideas given above regarding the combination of the lipomas and the anomalies in the present case in view of the temporal sequence.

As to angiographic findings of intracranial lipomas, dilatation and tortuosity of the feeding arteries associ- ated with tumor stain are often seen in the literature particularly in cases of lipomas located in the callosal cistern and sylvian fissure [17,22,23,28]. However, find- ings of lipomas on the cerebral surface have not been well documented so far. Britt et al. [11] only stated the abnor- mal vascularity as the angiographic findings with neither details nor photographs, while cerebral angiography was not performed in the other 3 cases reported over the cerebral surface. In the present case, similar to some cases of sylvian lipoma [6,17] and compatible with the report by Britt et al. [11], dilatation and tortuosity of the feeding arteries, angiomatous tumor blushes, hypovas- cularity in the surrounding areas, and dilated bridging veins draining the areas around the tumors were seen characteristically. We suppose that these angiographic findings observed should be noted, because it is likely that they might be among the radiological features of the lipomas on the cerebral surface, especially when in asso- ciation with gray matter infoldings, and the presence of the findings could be of significance and value in diagno- sis. Further reports of similar cases are required to con- firm this idea.

Acknowledgements

We are indebted to Dr. H. Shiga and Dr. S. Mo- moshima (Department of Radiology, School of Medi- cine, Keio University) for neuroradiological consulta- tion; and Dr. Y. Ogawa (Department of Pathology, Saitama Children's Medical Center) for the histopathol- ogical study.

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