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NEURORADIOLOGY Table of Contents   
Year : 2006  |  Volume : 16  |  Issue : 3  |  Page : 303-304
An unusual cerebello-medullary angle mass - case report


Departments of Neurological Sciences and Radiodiagnosis, Christian Medical College, Vellore 632004, Tamilnadu, India

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Keywords: Primary Melanoma, CNS, Cerebellomedullary region

How to cite this article:
Sumit T, Samson G, Rao A, Haran R. An unusual cerebello-medullary angle mass - case report. Indian J Radiol Imaging 2006;16:303-4

How to cite this URL:
Sumit T, Samson G, Rao A, Haran R. An unusual cerebello-medullary angle mass - case report. Indian J Radiol Imaging [serial online] 2006 [cited 2020 Feb 21];16:303-4. Available from: http://www.ijri.org/text.asp?2006/16/3/303/29001

   Introduction Top


Primary melanomas most commonly originate in the skin, mucosa, and the choroid in the eyes. In most instances, melanoma involving the CNS represent metastatic disease. Melanoma is the most common primary tumor to produce brain metastases, after lung and breast cancers. We report an unusual site of primary melanoma in the right cerebellomedullary and cerebellopontine angle with different imaging features


   Case report Top


A fifty five year old man presented with history of decreased sensations on the right side of the face, decreased hearing in the right ear, nasal regurgitation and imbalance of gait for six months. On examination he had bilateral horizontal gaze evoked nystagmus, right V, VII, VIII, IX and X cranial nerve palsies and signs of cerebellar dysfunction on the right. CT scan showed a hyperdense, 5 x 3.5 x 3.5 cm contrast enhancing mass in the right cerebellomedullary and cerebellopontine cisterns with areas of chunky calcification [Figure - 1]. MRI scan showed an extra axial lesion in right cerebellomedullary and cerebellopontine regions that was hyperintense on T1W images [Figure - 2]. The lesion was isointense to hypointense on T2W images [Figure - 3] and showed moderate enhancement on the post contrast images [Figure - 4]. There were foci of hypointensities on both T1 and T2 weighted sequences corresponding to the calcification seen in the CT scan. Angiography showed a diffuse tumor blush in the posterior fossa, fed by right ascending pharyngeal artery. MRI signal morphology was favouring Melanoma. Plain radiograph of chest and Ultrasonogram of abdomen were normal. Biochemical parameters were within normal limits. He underwent right retromastoid suboccipital craniectomy and subtotal excision of the lesion. Intraoperatively the surface of the cerebellum appeared xanthochromic and there were streaks of black colored tissue on it. There was a large firm vascular black mass in the right cerebellopontine and cerebellomedullary cisterns with numerous arterialised veins on its surface. Histopathology was reported as melanocytoma


   Discussion Top


Tumours of the cerebellopontine angle (CPA) are frequent; acoustic neuromas and meningiomas represent the great majority of such tumours. However, a large variety of unusual lesions can also be encountered in the CPA. The site of origin is the main factor in making a preoperative diagnosis for an unusual lesion of the CPA. A close association between CT and MR imaging findings is very helpful in establishing the preoperative diagnosis for unusual lesions of the CPA. One of the such unusual lesion in the CPA is melanoma.

Most patients with primary CNS melanomas are in the fourth decade of life, and specific monoclonal antibodies in CSF are present in 95% of them.[1] Melanotic tumours in the central nervous system include primary or metastatic melanomas, melanotic schwannoma, melanotic neuroectodermal tumour and meningeal melanocytoma.[2] The meningeal melanocytoma arises from the melanocytes occurring in normal leptomeninges. These leptomeningeal melanocytes are derived from the neural crest elements normally found within the basal layer of the epidermis and the leptomeninges covering the base of the brain and the brainstem [3]. The largest concentration of melanocytes is on the pia surrounding the medulla (particularly ventrally) and on the high aspect of the cervical spinal cord and may be visible on T2-weighted MR images as areas of low signal intensity, mostly on the ventral surface of the medulla.[4] Meckel's cave is the second most common location.[5]

At CT, primary melanocytic lesions appear as well-circumscribed, isoattenuating to hyperattenuating extra axial tumors with homogeneous enhancement. Even if there is no hyperostosis, they can mimic a meningioma. In this case, the unusual feature was calcification within the tumour. The signal changes in T1 and T2 weighted MR sequences may be opposite to that usually seen with most intracranial tumours.The MRI appearance of the meningeal melanocytoma is not uniform and depends on the degree of melanisation and hemorrhage within the tumour.[6],[7] Melanin results in T1 and T2 shortening because of the presence of stable free radicals within it. Unpaired electrons in melanin and water protons produce a dipole-dipole interaction that results in high T1 and low T2 signal intensity.[8] Therefore, melanocytic neoplasms are isointense or hyperintense to adjacent normal brain tissue on T1-weighted images and isointense or hypointense on T2-weighted images. They enhance after intravenous administration of contrast material. The prognosis is quite good in most cases. The mainstay of treatment for mucosal melanoma is surgical resection

 
   References Top

1.Nicolaides P, Newton RW, Kelsey A. Primary malignant melanoma of meninges: atypical presentation of subacute meningitis. Pediatr Neurol 1995; 12:172-174  Back to cited text no. 1  [PUBMED]  [FULLTEXT]
2.Winston KR, Sotrel A, Schnitt SJ. Meningeal melanocytoma. Case report and review of the clinical and histological features. J Neurosurg 1987; 66:50-57.  Back to cited text no. 2    
3.Faillace WJ, Okawara SH, McDonald JV. Neurocutaneous melanosis with extensive intracerebral and spinal cord involvement. J Neurosurg 1984; 61:782-785.  Back to cited text no. 3  [PUBMED]  
4.Gebarski SS, Blaivas MA. Imaging of normal leptomeningeal melanin. AJNR Am J Neuroradiol 1996; 17:55-60  Back to cited text no. 4  [PUBMED]  [FULLTEXT]
5.Prabhu SS, Lynch PG, Keogh AJ, Parekh HC. Intracranial meningeal melanocytoma: a report of two cases and a review of the literature. Surg Neurol 1993;40:516-521.  Back to cited text no. 5  [PUBMED]  
6.Woodruff WW Jr, Djang WT, Mclendon RE, et tal. Intracerebral malignant melanoma: high-field-strength MR imaging. Radiology 1987;165:209-213.  Back to cited text no. 6    
7.Edward J. Escott, MD. A Variety of Appearances of Malignant Melanoma in the Head: A Review1 Radiographics 2001; 21:625-639.  Back to cited text no. 7    
8.Rubino GJ, King WA, Quinn B, Marroquin C, Verity MA. Primary pineal melanoma: case report. Neurosurgery 1993;33:511-515  Back to cited text no. 8    

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Correspondence Address:
G Samson
Department of Neurological Sciences, Christian Medical College and Hospital, Vellore-632004
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-3026.29001

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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]



 

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