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|Year : 2018 | Volume
| Issue : 5 | Page : 1518-1520
Distal Sylvian fissure lipoma masquerading as a vascular malformation with bleed
Mustafa Iqbal Ahmed Chandshah1, Nishanth Sadashiva1, Jitender Saini2, Dhaval Shukla1
1 Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bengaluru, Karnataka, India
2 Department of Neuroimaging and Interventional Radiology, National Institute of Mental Health and Neurosciences, Bengaluru, Karnataka, India
|Date of Web Publication||17-Sep-2018|
Dr. Dhaval Shukla
Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bengaluru - - 560 029, Karnataka
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Ahmed Chandshah MI, Sadashiva N, Saini J, Shukla D. Distal Sylvian fissure lipoma masquerading as a vascular malformation with bleed. Neurol India 2018;66:1518-20
Intracranial lipomas are uncommon lesions with an incidence of 0.1–1.7% amongst all intracranial tumors. The distribution of intracranial lipomas in the order of incidence is as follows: interhemispheric fissure (47%), quadrigeminal/superior cerebellar cistern (25%), suprasellar/interpeduncular cistern (14%), cerebellopontine cistern (9%), and Sylvian cistern (5%). If incidentally detected, most cases do not require any treatment. Here, we present a case of a Sylvian fissure lipoma, which was masquerading as an arteriovenous malformation with bleed.
An 11-year old boy presented with generalized seizures of 6 month duration. He never had an episode of headache, vomiting, or loss of consciousness in the past. His developmental milestones were normal but he was considered dull in studies. He was evaluated with a magnetic resonance imaging (MRI) at a local hospital, which reported the presence of a right parietal lobe lesion containing blood vessels. The lesion was hyperintense on T1- and T2-weighted imaging. The initial diagnosis was that of an arteriovenous malformation (AVM) with late subacute bleed. As the MRI study was incomplete, we repeated it with other sequences and thin sections. The repeat MRI showed the lesion in the distal Sylvian fissure. The M2 and the M3 segments of the middle cerebral artery (MCA) and angular artery were dilated, and the posterior branch of the angular artery had focal narrowing suggestive of a dysplastic MCA [Figure 1]. No AVM was seen. The lesion showed signal suppression on fat-saturated sequences, without any diffusion restriction. Susceptibility-weighted images showed the lesion to be homogenously hypointense. The final diagnosis of a Sylvian fissure lipoma was made. The patient was started on antiepileptic medications and is seizure-free at a follow-up of 2 years.
|Figure 1: (a) T1-weighted magnetic resonance imaging showing a kidney-shaped hyperintense lesion near the right Sylvian fissure;(b) the lesion is hyperintense on T2-weighted axial image; (c) on sagittal image, the lesion is associated with large dilated vessels on its lateral aspect at the Sylvian fissure; (d) the lesion is hypointense on fluid attenuated inversion recovery (FLAIR) image; (e) the lesion is hypointense on susceptibility-weighted image (SWI);(f) Postcontrast sagittal image showing the hyperintense lesion along the dilated vessels|
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Intracranial lipomas are rare and are often detected incidentally and managed conservatively. The Sylvian fissure lipomas are the least common of all intracranial lipomas, and only 13 cases have been reported previously. Intracranial lipomas are thought to develop from the abnormal persistence and maldifferentiation of the meninx primitiva during the formation of the subarachnoid cisterns. The presence of a lipoma may interfere with the development of adjacent cortical tissue during the ongoing formation of the Sylvian fissure. Associated brain malformations are seen in 55% of the patients, which include agenesis/dysgenesis of the corpus callosum, absent septum-pellucidum, cranium-bifidum, spina-bifida, encephalocele, myelomeningocele, hypoplastic vermis, and cortical dysplasia. In 36% of the lesions, traversing intracranial vessels and nerves are present. The explanations for the presence of the abnormal vasculature are: a. Congenital structural deficiency, as the artery shares the same malformative origin; b. Secretion of tumoral factors which weaken the arterial wall; and, c: The lipoma itself causes degeneration of the arterial wall by interfering with the arterial nutrition.
The most common symptom is epilepsy. If the lesion is diagnosed incidentally, the patient should be managed expectantly. The epileptogenic focus only occasionally corresponds to the lipoma. The main culprit may be the underlying cortical dysplasia or an associated anomaly in more than 50% of cases of symptomatic patients. In our case, no evidence of cortical dysplasia or any other coexistent congenital anomaly was seen.
On a computed tomographic scan, a lipoma appears as a well-defined homogeneous lesion with a density between −40 to −100 Hounsfield Units. Calcification may be seen. There is no contrast enhancement except in the angiomatous variety. The MRI signals for lipomas are typically similar to other adipose-rich tissues, i.e., the signals are hyperintense on T1- and T2-weighted sequences with signal suppression on fat-saturated sequences. On diffusion-weighted imaging (DWI), due to the presence of fat content, there is a restriction of diffusion. The most relevant differential diagnosis is a mature dermoid, but the latter entity is usually heterogeneous, reflecting the multiple tissue components present within it, whereas lipomas are homogenous and lobulated. Lipomas are infiltrative and may encase vessels as well as nerves and may also invade and adhere to the underlying brain, but dermoids are encapsulated with an outer wall of stratified squamous epithelium that expands and displaces the neighboring structures. An atypical epidermoid can be confused with a lipoma if the lesion shows T1 shortening, but it does not demonstrate chemical shift artifact and the signal does not suppress after the fat-saturation pulse. Diffusion weighted imaging (DWI) reveals epidermoids as hyperintense lesions relative to the brain and cerebrospinal fluid with diffusion restriction.
Though our case was initially thought to be an AVM based on the MRI signal characteristics of late subacute bleed and associated vascular changes, the detailed and more comprehensive MRI sequences revealed the actual pathology to be a lipoma, which was managed conservatively with a good result at a follow-up of 2 years. On routine MRI, a lipoma may be confused with a hematoma particularly when it is closely associated with abnormal vasculature.
To conclude, Sylvian fissure lipomas are rare. This entity should, however, be kept in mind whenever a lesion is seen on MRI to be close to the Sylvian fissure and is hyperintense on both T1 and T2-weighted sequences.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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Conflicts of interest
There are no conflicts of interest.
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