Cerebello pontine angle lipoma in a child.

Dear Sir,

Vestibular schwannomas, meningiomas, and epidermoids are the vast majority of the lesions occurring in the cerebello pontine angle (CPA). Exophytic brain stem tumors also often present in children as CP angle masses. Neoplastic and nonneoplastic pathologies other than these tumors constitute less than 1% of all lesions located in the CPA. Intracranial lipomas are rare and presumably maldevelopmental rather than being neoplastic in origin.[12] They arise from abnormal differentiation of the primitive meninx,[3-5] Clinically, CPA lipomas can cause slowly progressive neurological symptoms and signs related to cranial nerves or brain stem.[6-8] Although the CT findings of CPA lipomas can be typical, the magnetic resonance (MR) imaging, especially the fat suppression sequences, has improved the identification of these lesions.[33]The aim of this paper is to share our experience in the treatment of a rare lesion of the CPA.

A 5-year-old boy was evaluated for recurrent primary generalized seizures of 20 days duration. He had preceding headache, vomiting for which he was subjected to a Magnetic resonance imaging (MRI) scan of the brain. Imaging studies revealed a hyperintense mass in the right CPA suggestive of lipoma/epidermoid. He was referred to us for further management.

Basic routine blood investigations were essentially normal. His vital parameters were stable. He was conscious, oriented, and obeying commands. Child was active and had no motor/sensory/cranial nerve deficits. Plantars were bilaterally flexor with normal deep tendon reflexes. MR imaging has now achieved a very high sensitivity and specificity for detecting lipomas. On T1-weighted MR images, lipomas typically appear hyperintense compared with brain tissue and hyperintense on T2-weighted MR images. MRI scan of the brain was done and the findings is given below.

Multiplanar, multisequences, MR imaging, including SE T1 axial, flair axial, FSE T2 axial were done. Postcontrast T1-weighted multiplanar sequences were also performed.

A 17mm (trans) ×15mm (AP) × 15mm (CC) well-encapsulated mass lesion noted in the right CP angle which was hyperintense on T1, T2, and FLAIR with inversion on fat suppression sequence. The lesion was situated inferior to the right Vth nerve and indenting upon right lower pons and medulla. The right VIIth and VIIIth nerves and superior cerebellar artery were encased by the lesion. No evidence of tumor extension into IAC was noted [Figure 1]. There was neither significant shift nor hydrocephalus. Right cerebello pontine angle tumor–lipoma/epidermoid.

Figure 1

Magnetic resonance imaging revealing right CP angle lesion lipoma epidermoid

A right retro sigmoid suboccipital approach was chosen to expose the tumor. The lesion was extra-axial, yellowish and surrounding the seventh and eighth nerve complex. Branches of the AICA were embedded in the tumor. The lesion was partially decompressed. Neurovascular structures were preserved. There were no postoperative deficits.

Histopathological evaluation revealed it to be lipoma-right CP angle [Figure 2].

Figure 2

Histopathology showing features of lipoma

Intracranial lipomas are rare lesions, corresponding to less than 0.1% of all intracranial tumors.[69-14] These patients are most likely to present with slowly progressive symptoms of VIII nerve impairment and of trigeminal irritation.[5] These are results of long-standing nerve affection. These lesions are supposed to originate from persistence of the primitive meninx, a precursor of pia mater and arachnoid which develop into fat.[4] These tumors can cause symptoms related to the VIII nerve involvement, such as hearing loss, tinnitus, and vertigo. However, trigeminal symptoms such as neuralgia, paresthesia or headache, can also occur with CPA lipomas extending to the trigeminal cisterns.[56815]

Our patient presented with headache, and seizures. Neuroimaging revealed a hypodense mass in the right CPA suggestive of lipoma/epidermoid. He underwent surgical exploration and decompression of the tumor. Histopathology confirmed it as lipoma. The most common extra-axial sites for intracranial lipomas are the Sylvian cistern and CP angle. The latter is the most common in the posterior fossa, harboring 6–12% of all intracranial lipomas.[41617] Reviews of CPA tumors 20–30 years ago did not mention lipomas at all. In recent survey they seem to account for less than 1% of all CPA tumors, including all unusual lesions.[1318-21] The incidence of lipoma among the CPA space-occupying lesions is around 0.05%. The patients are most likely to present with slowly progressive symptoms of VIII nerve impairment and of trigeminal irritation. These are the results of long-standing nerve affection. Neuroimaging alone should establish the diagnosis with sufficient accuracy. The importance of neuroradiological establishment of diagnosis cannot be overemphasized because modern microneurosurgery does not result in a lipoma removal without causing additional cranial nerve damage and morbidity. In this child surgery was indicated due to the symptoms and also to confirm the diagnosis. From a surgical perspective, lipomas act as true tumors.[2223] Moreover, they are strikingly adherent to surrounding structures, encasing vessels and nerves rather than merely displacing. Pathology demonstrates a thorough infiltration of the adipose tissue within the nerve bundles and in between the single fascicles.[324-29] This infiltration likely accounts for the poor outcomes that follow attempts to dissect the tumor away from the nerves. Therefore conservative treatment options should be encouraged. There is, however, an indication for minimal surgical intervention in patients with intractable trigeminal neuralgia or if there are compressive symptoms of cranial nerves or brainstem.[30-37] In such situations careful nerve decompression may alleviate the symptoms. We therefore recommend follow-up of patients with a suspected lipoma by serial neuroimaging. If the patient is symptomatic or there is convincing growth surgical intervention can be considered.[3839]

We wish to thank and acknowledge Ms. Krithika Kalro, Ms. Rukmini, Ms. Denet Pradeep, and Ms. Jyothi for their help in preparing and submitting this paper.