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Editor,—Ultrasonography is useful in the diagnosis, treatment, planning, and monitoring of intraocular tumours. An important step in the diagnostic process is the differentiation between solid and cystic tumours. Uveal melanomas are usually solid but may rarely be cystic (W R Lee, personal communication). Cases have been reported in which pseudocystic appearances on ultrasonography have been due to haemorrhage or necrosis.1-3 We report a patient who appeared to have a cystic tumour on B-scan ultrasonography, which was shown on histology to be due to a very lightly pigmented nodule in a deeply pigmented melanoma.
The patient, a 56-year-old Asian man, was referred to St Paul’s Eye Unit from Taiwan for investigation and treatment of a choroidal tumour in the right eye. He presented with a 16 week history of blurred vision and visual field loss in the affected eye. Systematic inquiry revealed no other abnormalities. On examination, the vision was 6/12 in the right eye and 6/6 in the left eye. There was a relative afferent pupil defect in the right eye. The anterior segments and intraocular pressures were normal. The right posterior segment showed a large, pigmented choroidal tumour temporally, extending from the ora serrata to the temporal macula. This was associated with an exudative retinal detachment. The left fundus was healthy. B-scan ultrasonography showed the tumour to have sagittal and transverse basal dimensions of 17.2 mm by 16.6 mm, with a thickness of 11.3 mm. The internal tissue reflectivity suggested the presence of a large thin walled cyst (Fig1).
Trans-scleral local resection4 was performed and the tumour was examined by light microscopy after staining with haematoxylin and eosin in the conventional manner (Fig 2). On low power examination the tumour was shown to be entirely solid, with the pseudocystic area corresponding to a lightly pigmented nodule within a deeply pigmented tumour. High power microscopy, after melanin bleaching, revealed that the peripheral, very heavily pigmented tumour was of epithelioid cell type and the pseudocystic, lightly pigmented area consisted of spindle B type cells. There were no areas of necrosis and only a few small areas of haemorrhage.
Uveal melanomas are only rarely cystic. A pseudocystic appearance on B-scan ultrasonography of a solid uveal melanoma is an uncommon phenomenon and has been previously attributed to local areas of haemorrhage or necrosis.1-3 This is the first published case in which local variations in pigmentation of the tumour alone might account for the B-scan pseudocystic appearance. The acoustically silent area, mimicking a cystic cavity, was composed of cells that were both amelanotic and spindle-shaped. It is not possible, therefore, to determine which of these two features was responsible for the ultrasonographic appearances. Despite the difference in the cell type of the central and peripheral areas of the tumour, the most striking abnormality is the difference in pigmentation. An A-scan may allow differentiation between a pseudocyst and a true, haemorrhagic cyst by showing after-movement of spikes in the true cyst.1 In conclusion, a solid uveal melanoma may falsely appear cystic on B-scan ultrasonography if it contains a nodule of non-reflective tissue.