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Year : 2016  |  Volume : 64  |  Issue : 1  |  Page : 152--154

Squash cytopathology of primary meningeal melanocytoma

Aniket Halder, Saikat Bera, Chhanda Datta, Uttara Chatterjee, Manoj Kumar Choudhuri 
 Department of Pathology, Institute of Postgraduate Medical Education and Research, Kolkata, West Bengal, India

Correspondence Address:
Uttara Chatterjee
57/11A, Ballygunje Circular Road, Kolkata - 700 019, West Bengal

How to cite this article:
Halder A, Bera S, Datta C, Chatterjee U, Choudhuri MK. Squash cytopathology of primary meningeal melanocytoma.Neurol India 2016;64:152-154

How to cite this URL:
Halder A, Bera S, Datta C, Chatterjee U, Choudhuri MK. Squash cytopathology of primary meningeal melanocytoma. Neurol India [serial online] 2016 [cited 2021 Nov 27 ];64:152-154
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Meningeal melanocytomas (MMs) are benign pigmented tumors of the central nervous system (CNS) that originate from the leptomeningeal dendritic melanocytes. These tumors, together with primary malignant melanomas, meningeal melanocytic nevi, pigmented meningiomas, pigmented schwannomas or neurofibromas, pigmented primitive neuroectodermal tumors, and meningeal melanoblastomas, make up the group of primary melanocytic neoplasms of the CNS.[1] Melanocytes in the CNS are usually found at the base of the brain, brain stem, and spinal cord. MMs account for 0.06%–0.1% of brain tumors, and their incidence is 1 in 10 million. They commonly affect adults aged 45–50 years, with a slight female predominance (1.5:1).[2] Most of them are solitary with a slow growth and a long clinical course. However, there are reports of their transformation to malignant melanoma and leptomeningeal dissemination.[3],[4] Most of the available literature on MMs is based on histopathological diagnosis, without elaboration of their cytological features seen on intraoperative squash smear. Here we present the report of a man with a leptomeningeal MM and describe the cytomorphology of this tumor, along with its differential diagnoses.

A 20-year-old man presented with headache and intermittent vomiting for 8 months. He also complained of progressive blurring of vision of both eyes. Ophthalmic examination revealed decreased visual acuity of both eyes and bilateral papilledema. Neurological examination was otherwise normal, and other laboratory results were unremarkable. There were no associated comorbidities.

MRI showed a well-defined, heterogeneously enhancing solid extra-axial mass in the parieto-occipital lobe, measuring 71 × 6 × 54 mm, with a high signal intensity on T1 images. There was evidence of intratumoral hemorrhage and perilesional edema. In addition, there was compression and displacement of the left occipital horn along with herniation of the cerebellar tonsils. Radiologically, a diagnosis of meningioma was considered [Figure 1].{Figure 1}

Intraoperatively, the mass was found to be supratentorial. It was soft and moderately vascular. A gross total resection and histopathological examination of the lesion was performed.

The squash smear spread easily, and on holding up against light, it showed fine clumps against a dark background. The usual crunch and grit, found while making smears in the cases with a meningioma, was lacking. The black granularity and the dark background were also evident on the stained smears [Figure 2].{Figure 2}

Microscopically, the tumor was composed of dyscohesive clumps of large polygonal cells. The cells were heavily pigmented obscuring the nuclear details. The pigment appeared to be coarse, brown, and nonrefractile. There were numerous thin-walled blood vessels criss-crossing the smears, surrounded by pigment-laden cells [Figure 3]. However, evidence of endothelial proliferation was lacking. Mitotic figures, necrosis, or significant pleomorphism were not seen. Based on these features, an intraoperative diagnosis of melanocytoma was offered.{Figure 3}

The entire mass was resected. The specimen consisted of several fragments of coal-black, soft, and friable tissue measuring approximately 10 cm 3 altogether. Microscopically, the tumor was heavily pigmented, cellular, and biphasic, consisting of spindle cells and epithelioid cells. The spindle cells were arranged in tight nests with a vague whorling pattern, and heavily pigmented cells were seen at the periphery of the nests. The epithelioid cells were arranged in vasocentric fascicles and were packed with brown-black pigment. The pigment-laden cells showed a perivascular arrangement [Figure 4]. However, nuclear pleomorphism, mitosis, necrosis, or hemorrhage was lacking. Evidence of endothelial proliferation and brain invasion was not observed, and a diagnosis of meningeal melanocytoma was considered [Figure 5]. The tumor cells showed strong immunoreactivity for S-100 but were negative for glial fibrillary acidic protein (GFAP), and the diagnosis of meningeal melanocytoma was confirmed [Figure 6]. The postoperative period was uneventful. He has been followed up for a period of 6 months, during which he has remained symptom free.{Figure 4}{Figure 5}{Figure 6}

Primary melanocytic neoplasms are rare lesions that originate from leptomeningeal melanocytes.[5] There are three main types of melanocytic lesions of the CNS, including diffuse melanocytosis, meningeal melanocytoma, and primary malignant melanoma.[6] The first description of meningeal melanocytoma was in 1972 by Limas.[7] Neurological features in meningeal melanocytoma include raised intracranial tension, hydrocephalus, seizures, basal meningitis, cranial nerve palsies, psychiatric disturbances, and myeloradiculopathy.[8] Classically, MMs are iso- to hyperattenuating lesions with a variable contrast enhancement that is detectable on CT images. MRI of these lesions show a high signal intensity on T1-weighted images, diminished signal on T2-weighted images, and diffuse enhancement after contrast.[5],[6]

Considering the rarity of this neoplasm and paucity of published literature, the intraoperative diagnosis of MMs is a challenge to cytopathologists. Melanocytomas are usually diagnosed on histological examination, and data on cytological details of the same are scarce. Only two cases have been described in the literature as a part of the squash cytology series; however, the details of the cytological findings in these cases have not been dealt with.[9],[10] Melanocytoma is a rare tumor, and hence, one must be aware of the light microscopic features of this tumor both on cytologic smears and histology. MM is a pigmented lesion, and hence, the differential diagnoses include other pigmented CNS tumors such as malignant melanoma, melanotic medulloblastoma, melanotic ependymoma, melanotic schwannoma, and melanotic meningioma.[11] The possibility of malignant melanoma is excluded because a melanocytoma lacks nuclear atypia, mitotic activity, apoptosis, and necrosis. Medulloblastomas have small round-cell tumor morphology and are mitotically active. Ependymomas occur at spinal locations and are excluded based on their typical cytologic features of bristle-like arrangement of cells attached to short thick blood vessels. Melanotic schwannomas do not spread easily on smears and show bridges of cohesive spindle cells. Meningiomas, like schwannomas, are also difficult to spread. Presence of cohesive cells with broad cytoplasmic processes, whorls, and psammoma bodies is characteristic of meningiomas. In the angiomatous type, the presence of abundant hemosiderin pigment may cause diagnostic difficulty; however, careful evaluation of the cytological details is helpful.

The large majority of melanocytomas contain abundant melanin pigment both within the tumor cells and the coexisting melanophages, which are strongly immunoreactive for S-100, HMB-45, and Melan-A, but are negative for GFAP and epithelial membrane antigen (EMA).[12] In our case, the tumor cells showed a strong S-100 immunoreactivity and negative GFAP staining, which confirmed the diagnosis.

Despite its benign appearance, meningeal melanocytoma may follow an aggressive course, with recurrences occurring within 6 months to 5 years. Gross total resection is the treatment of choice. Accurate diagnosis of this condition on squash preparations is important, as it guides the clinician in making an intraoperative decision in favor of gross total resection.

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