Choroidal Schwannoma: Immunohistochemical and Electron-Microscopic Study

Abstract

Schwannoma (neurilemoma) arising from the ciliary body and choroid is a rare form of intraocular tumor and usually misdiagnosed clinically as amelanotic melanoma. This case report describes a 73-year-old woman who developed a large nonpigmented intraocular tumor of the choroid in the left eye and underwent enucleation with a clinical diagnosis of malignant melanoma. The tumor consisted of spindle-shaped cells with an indefinite cytoplasm and twisted nuclei, which had positive immunoreactivity for S-100 protein, vimentin, glial fibrillary acidic protein and neural cell adhesion molecule. A continuous basal lamina encompassing the tumor cells was demonstrated by immunostaining for laminin and type IV collagen. Ultrastructurally, tumor cells with scant organelles had delicate cytoplasmic processes apposing each other, all indicative of Schwann cell origin. In reexamination of fluorescein angiograms, ultrasonograms and magnetic resonance images, no findings were incompatible with a diagnosis of choroidal melanoma. Histopathological studies showed that the tumor was a schwannoma. At present, we do not have a benchmark for the clinical diagnosis of intraocular schwannoma.

Intrasclera schwannoma

“…Another interesting point is that the MRI showed ring enhancement which is less consistent with the diagnosis of melanoma or metastasis. Because of low index of suspicion, this type of tumour usually is misdiagnosed5–7 as in our case. While T1 and T2 weighted MRI images are routinely used to diagnose intraocular tumours, newer methods like magnetic resonance spectroscopy could be considered in atypical cases to provide in vivo metabolic information of the tumours; this procedure has been shown to be effective in differentiation between benign and malignant orbital lesions in 93.7% of cases 8.…”

“…In the latter case, differentiation with amelanotic melanoma or other choroidal tumours is difficult 5. Misdiagnosing schwannoma for amelanotic melanoma is reported by Matsuo et al 6. They have reported a 72-year-old woman who's left eye was enucleated with diagnosis of melanoma for which all the histopathologic studies were in favour of schwannoma.…”

Choroidal schwannoma: a case series of five patients

“…Light microscopy usually reveals a tumour composed of spindle cells with bland nuclei 13. Two main growth patterns are seen: first, Antoni A tissue, in which there is a dense accumulation of elongated cells, often with nuclear palisading (so-called Verocay bodies, as seen in case 4) and, second, Antoni B tissue, where cells are less densely arranged in a loose myxoid matrix, within which xanthoma cells may be present.…”

“…Long-spaced collagen (‘Luse bodies’) are also present 13. In the pigmented and melanocytic variants, numerous melanin granules are seen.…”

“…In the melanocytic variant, features of melanogenesis can be observed (melanosomes in varying stages of melanisation, fine cytoplasmic filaments and micropinocytotic vesicles). Immunohistochemically, the spindle cells of schwannomas are positive for S-100P and vimentin 13. With the exception of the melanocytic and pigmented variants, they are usually negative for the melanocytic markers, MelanA and HMB45.…”