The patient is a 50 year old man with no ophthalmic history. He presented with a nasal subconjunctival lesion, present for 18 months.
The submitted specimen measured less than 1mm.
Figure 1. (H&E, x10 objective)
Figure 2. (neurofilament, x10 objective)
What are the histological features?
The lesional tissue was strongly positive with S100. Figure 2 is the neurofilament immunohistochemistry. What is demonstrated?
What is the diagnosis?
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This is a collection of spindle cells with architecture reminiscent of neural tissue. A few pigmented melanocytes are seen at the periphery (confirmed with Melan A)
The neurofilament demonstrates axonal fibres scattered throughout the specimen.
Intrascleral nerve loop (of Axenfeld).
Intrascleral nerve loops are usually incidental findings, and the opportunity to examine them histologically is rare.. Occasionally one is visible on clinical examination, and biopsied (fortunately rarely!).
They are said to be very painful on manipulation, although no comment was made regarding pain in this case. As they are associated with melanocytes, there may be clinical suspicion of melanoma.
The differential diagnosis of subconjunctival spindle cell lesions includes melanocytic and neural proliferations, as well as entities such as spindle cell carcinoma, rhabdomyosarcoma and vascular tumours. In this case, the immediate impression was that this was a nerve rather than a neoplasm, although schwannoma and neurofibroma were also considered. The compact character and palisading of schwannoma were not present. The wavy nuclei of neurofibroma were not prominent and the diffuse S100 positivity was also against neurofibroma.
Crandall, A. S., Yanoff, M. & Schaffer, D. B. Intrascleral nerve loop mistakenly identified as a foreign body. Arch. Ophthalmol. 95, 497–498 (1977)
Harry, J. & Misson, G. P. Clinical Ophthalmic Pathology: Principles of diseases of the eye and associated structures. (Butterworth Heinemann: Oxford, 2001) p178
Lee, W. R. Ophthalmic Histopathology. (Springer-Verlag: London, 1992) p348