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Tapioca melanoma of the iris

Tapioca melanoma of the iris is a form of diffuse iris melanoma, so named for its macroscopic resemblance to tapioca pudding. A rare variant of iris melanoma, this condition usually presents as unilateral hyperchromic heterochromia and often causes glaucoma via obstruction of aqueous outflow. Typically, it is characterised by diffuse, circumferential neoplastic involvement of the iris and anterior chamber angle and may involve the ciliary body. It is not clear whether the tumour arises from the iris or the ciliary body. Clinical differentiation between benign and malignant iris lesions can be challenging. Histological and immunohistochemical confirmation via a tissue biopsy is often required. Histologically, tapioca iris melanomas are composed of poorly pigmented spindle or epithelioid malignant cells with a diffuse growth pattern. Local invasion of adjacent ocular structures is common and distant metastasis, usually to the liver, has been reported. A 16-year-old Caucasian male presented with a one-year history of left iris hyperchromic heterochromia and occasional blurred vision. An intermittent left-sided headache had developed a few weeks prior to presentation. He had a family history of cutaneous melanoma in his mother and maternal aunt. Uncorrected vision was 6/6 bilaterally and there was no evidence of an afferent pupillary defect. On external observation, heterochromia was apparent, with a green right iris and a brown left iris. Biomicroscopy of the left iris revealed multiple small, pigmented nodules involving the entire anterior surface and a non-cohesive pseudohypopyon (Figure 1). The right iris appeared normal. Intraocular pressures were 12 mmHg in the right eye and 29 mmHg in the left with Goldmann applanation tonometry. The left iris was diffusely vascularised with a poorly reactive pupil and 2+ white cells were visible in the anterior chamber. Gonioscopy revealed open angles, with 1+ angle pigmentation and visible nodules in the left angle. No ciliary body masses were evident through the dilated pupil. A dilated fundus examination demonstrated increased cupping of the left disc with otherwise normal anatomy and colour. The remainder of the posterior segment was normal.