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A 49-year-old white male was diagnosed with a pigmented iris nevus in his left eye, noted in early childhood and followed by serial photography and ultrasonography elsewhere. More recently, he complained of fluctuating vision and was found to have acquired left iris hyperchromatic heterochromia (Fig. 1A). One year prior to his referral, he had been diagnosed with unilateral pigmentary glaucoma with intraocular pressure (IOP) of 44 mmHg and had undergone trabeculectomy. He had not used prostaglandin analogues and his current treatment was a topical anticholinergic agent (pilocarpine) and a beta-blocker (betaxolol). The progressive nature of the heterochromia and pigment seeding into the trabeculectomy bleb prompted his referral. Radial keratectomy had been performed in both eyes 10 years previously.

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Figure 1.  Clinical features and fine-needle aspiration biopsy followed by resection of a necrotic iris melanocytoma causing a dark-brown filtering bleb. (A) External photograph demonstrating hyperchromatic heterochromia of the left eye (LE). (B) Slit-lamp photograph of the LE showing the necrotic iris melanocytoma inferonasally and pigment seeding on the iris surface. (C) Trabeculectomy bleb in the LE, showing clear cystic areas and solid pigment deposition. (D) The trabecular meshwork was densely pigmented in the angle. (E) Ultrasound biomicroscopy showed the solid tumour was confined to the iris. (F) Fine-needle aspirate of melanocytoma showing large heavily pigmented cells (partially bleached) with low nuclear cytoplasmic ratio. (Papanicolaou staining; original magnification × 250.) (G) Routine histological section through a viable part of the resected tumour showing heavily pigmented tumour cells replacing normal iris tissue. (Haematoxylin-eosin staining; original magnification × 100.). (H) Corresponding bleached section of viable part of tumour showing bland nuclei and low nuclear : cytoplasmic ratio consistent with melanocytoma. (Bleach; original magnification × 100.) (I) Routine section showing necrotic part of iris tumour. (Haematoxylin-eosin staining; original magnification × 100.) (J) Corresponding bleached section showing extensive tumour necrosis and infiltration by melanophages. (Bleach; original magnification × 100.)

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The right eye was normal, with 20/25 visual acuity (VA) and IOP of 12 mmHg. The left eye, with 20/20 VA, had IOP of 15 mmHg. The left iris had a dark-brown, pigmented mass inferonasally, 4 mm in diameter and 2 mm in thickness, which extended from the iris root to the pupillary margin (Fig. 1B). The surface was irregular with a central crater and there were no intrinsic or feeder blood vessels. In the superonasal quadrant of the conjunctiva was a filtering bleb with microcysts and brown pigment debris (Fig. 1C). Diffuse pigmented tumour seeds were found on the entire iris surface and in the trabecular meshwork (Fig. 1D). Ultrasound biomicroscopy confirmed a solid iris mass without posterior extension (Fig. 1E). The fundus was normal and the optic nerve showed a 0.4 cup : disc ratio. Transcorneal fine-needle aspiration biopsy of the lesion, carried out to rule out melanoma, revealed large, heavily pigmented cells (Fig. 1F). Bleached sections disclosed small, round and relatively uniform nuclei with indistinct nucleoli, consistent with melanocytoma. For longterm IOP control and to reduce further pigment deposition, tumour resection by basal iridectomy was performed. Microscopy disclosed an intensely pigmented neoplasm with extensive areas of necrosis infiltrated by melanophages (Fig. 1G−J). The residual viable cells showed bland nuclei and a low nuclear:cytoplasmic ratio.

Following resection, pigmentation in the filtering bleb decreased over 10 months, although topical antihypertensive medications were still required to maintain normal IOP.

Brown pigment within a filtering bleb is an ominous finding that, to our knowledge, has been reported only in the presence of melanoma of the iris or ciliary body (Grossniklaus et al. 1990; Pasternak et al. 2005). We present an unusual case of pigment seeding in a trabeculectomy bleb from benign melanocytoma, simulating malignant melanoma.

Iris melanocytoma, a magnocellular nevus, is a discohesive granular tumour that often disperses pigment on the iris and trabecular meshwork, resulting in raised IOP, which should be included in the differential diagnosis of unilateral pigmentary glaucoma (Shields et al. 1977; Fineman et al. 1998; Demirci et al. 2005). Pigment dispersion from an iris melanocytic tumour clinically suggests diffuse malignant melanoma, but it should be noted that benign necrotic melanocytoma can produce similar findings. In a previous report of 47 cases of iris melanocytoma, raised IOP was observed in 11% of cases at 10 years and 55% at 15 years (Demirci et al. 2005). Elevated IOP typically resolves over months with surgical resection of the tumour (Shields et al. 1977; Fineman et al. 1998).

If the fine-needle aspiration biopsy had shown melanoma cells, then enucleation, partial tenonectomy and orbital map biopsies would have been our favoured option. Fortunately, the tumour was benign and local resection was acceptable to prevent longterm deposition of pigment throughout the anterior chamber and iridocorneal angle.

This study was supported by a donation from Michael, Bruce and Ellen Ratner, New York, NY (JAS, CLS); the Paul Kayser International Award of Merit in Retina Research, Houston, TX (JAS); Mellon Charitable Giving from the Martha W. Rogers Charitable Trust (CLS); the Eye Tumor Research Foundation, Philadelphia, PA (CLS, JAS), and the Noel T. and Sara L. Simmonds Endowment for Ophthalmic Pathology, Wills Eye Hospital (RCE). MSS is supported by the Fulbright Fellowship in Cancer Research, the TFC Frost Trust and Special Trustees of Moorfields Eye Hospital, London, UK.

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