Abstract
Granular cell tumors of the central nervous system are rare tumors. To date, eight cases arising from cranial nerves have been reported. Granular cell tumors have also been found arising from the neurohypophysis and its stalk. Due to their rarity and histological similarity to other central nervous system (CNS) tumors with a granular appearance, they often pose a diagnostic conundrum. The differential diagnosis is surprisingly diverse and includes granular cell astrocytoma, infundibular granular cell tumor, spindle cell oncocytoma of the adenohypophysis, granular and oncocytic variants of pituitary adenoma, meningioma, pituicytoma and intrasellar schwannoma. Distinguishing between the CNS tumors with granular features is important because some tumors have an increased recurrence risk or a poor prognosis. To highlight the histological features of granular lesions of the central nervous system, including the immunohistochemical profile and electron microscopic depiction, we review two cases each with a similar granular histology and a different final diagnosis. Thorough online literature search revealed several cases of granular cell lesions of the CNS, however, oftentimes the diagnosis is difficult to come by and the differential is long. Conclusion: Granular cell tumor and its variants, though uncommon, must be included in the differential diagnosis of CNS lesions.
Highlights
Granular cell tumors of the central nervous system are rare tumors
The differential diagnosis must always include a true granular cell tumor when granular morphology is identified, especially when it encompasses a majority of the lesion
The hypothesis is that the granular cell phenotype seems to be not specific of a certain tumor type, but rather a peculiar change characterized by an increase in intracellular lysosomes
Summary
Granular cell lesions of the central nervous system (CNS) are rather uncommon and may pose a diagnostic challenge. Post contrast images demonstrated an intensely enhancing mass in the right middle cranial fossa that was hypointense on T2weighted images and isointense to adjacent gray matter on T1weighted images (Figure 1) It was centered in Meckel’s cave with involvement of the cisternal segment of the trigeminal nerve. Permanent section analysis revealed peripheral nerve and entrapped ganglion cells (trigeminal ganglion) infiltrated by round, spindled and epithelioid cells with abundant, granular, PASpositive cytoplasm consistent with granular cell tumor (Figure 5). The tumor cells were strongly positive for CD 68 with abundant PAS positive cytoplasmic granules and strong reactivity to S100 (Figures 6 and 7). They were non reactive for: synaptophysin, smooth muscle actin, muscle specific actin, melanA, myogenin, GFAP, smooth muscle myosin heavy, and desmin. Electron microscopy demonstrated tumor cell cytoplasm filled and expanded with dark, granular lysosomes, characteristic of granular cell tumor (Figure 8)
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