Several degenerative conditions predispose to retinal detachment. The separation between the neural retina and the retinal pigment epithelium can be caused by traction, exudate, or by so-called rhegmatogenous detachment. Traction detachment occurs when the vitreous shows fibrosis or gliosis, following trauma or by neovas-cularisation. Accumulation of fluid between the layers of the retina is called exudative detachment. It can be caused by processes with excessive permeability of reti-
Iris naevi present as pigmented macular lesions, are very slowly progressive, and often completely static over years. When the clinical presentation is not suspicious, in most cases the lesion will not be excised. For that reason, naevi of the uveal tract are most commonly incidental findings. Histology shows a symmetrical lesion, located in the anterior part of the iris stroma, and usually composed of small spindle cells with small, uniform nuclei. Large nucleoli and especially mitotic figures indicate a suspected malignant melanoma.
Fig. 10.20. Uveal tract melanoma: detail of closely packed spindle-shaped cells; in this area almost no pigment is present
In the ciliary body naevi are very rare; the histology is comparable with iris naevi: spindle-shaped cells without atypia and without mitotic figures. In the choroid, naevus cells are spindle-shaped and often heavily pigmented, nuclei are uniform, and no mitotic figures are seen. Depigmentation of the slides may be helpful in evaluating cytological details.
The major part of uveal tract melanomas arise in the choroid (Fig. 10.19). Most frequently affected are white individuals in the sixth and seventh decades of life. Most melanomas are single and confined to one eye. In most cases they arise from pre-existing naevi in the choroid. Ciliary body and iris melanomas are rare. Malignant melanoma of the choroid presents with loss of vision in one eye, or with secondary closed angle glaucoma. The glaucoma is caused by detachment of the retina with lens-pupil block. Spread of the tumour into the orbita can cause proptosis. The primary clinical differential diagnosis for melanoma is choroidal metastasis. At macroscopic examination of an enucleated eye with a choroidal melanoma, it is important to locate the tumour before cutting the eye. The tumour can be located by palpation and transillumination. If possible, the main histological section should contain the centre of the pupil, the optic nerve and the centre of the tumour. Small pigmented nodules can be seen on the external surface of the sclera in case of trans-scleral extension of the tumour. The sample taken at this point sometimes needs section at multiple levels to demonstrate the tumour passing through the scleral canals. Microscopically, the melanomas consist of
spindle-shaped cells, epithelioid cells, or a combination of both (mixed cell type). The spindle-shaped cells are closely packed elongated cells, often with pronounced nucleoli and a few mitotic figures. In epithelioid lesions, the cytoplasm is more eosinophilic and mitotic figures are easily found. Melanin pigment is usually is present, but amelanotic lesions can be seen (Figs. 10.20-10.23). Positive immunohistochemistry with S-100, melan A or HMB45 confirms the diagnosis in those cases. The final report should include the origin of the tumour (choroid, ciliary body, iris), the thickness of the tumour (in mm), the cell type (spindle cell type, epithelioid cell type or mixed cell type) and extraocular growth. The 5-year survival of pure spindle tumours is 80%, while pure epithelioid tumours have a 5-year survival of 35%. The 20-year survival of both groups is only 20%.
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Complete Guide to Preventing Skin Cancer. We all know enough to fear the name, just as we do the words tumor and malignant. But apart from that, most of us know very little at all about cancer, especially skin cancer in itself. If I were to ask you to tell me about skin cancer right now, what would you say? Apart from the fact that its a cancer on the skin, that is.