Brachytherapy and anterior segment imaging in iris melanoma.

Ultrasound biomicroscopy (UBM) remains a potent tool in the diagnosis and characterization of uveal lesions. In the setting of malignancy, it can confirm both placement of and response to brachytherapy. We present a case of iris melanoma with aggressive BAP-1 mutation, treated successfully with I-131 brachytherapy which was both characterized and followed with UBM and thereafter discuss the current state of these modalities.

Introduction

Uveal melanomas are the most common primary intraocular tumor in adults (annual incidence of 5.1/million), of which iris melanomas account for 3–10%.[1] The risk factors for uveal melanomas are predominantly nonmodifiable and include Caucasian descent, lighter iris color, and inactivation of the BAP1 gene occurring in 84% of metastasizing tumors.[2]

Case Presentation

A 40-year-old asymptomatic nonsmoking Caucasian male with no ocular history presented with a darkly pigmented infratemporal lesion in his right eye, first noticed 1 year before. The corrected visual acuity in both eyes was 6/6, intraocular pressure measured 15 and 16 mmHg in the right and left eyes, respectively, and both pupils were equal and reactive. Slit-lamp biomicroscopy showed a well-demarcated and heavily pigmented lesion in the peripheral iris between 6 and 8 O'clock [Figure 1]. Fundus examination was normal, and gonioscopic examination revealed total angle closure by the tumor for 2 h. The estimated basal diameter for this elevated lesion measured at 4 mm × 2.5 mm [Figure 2].

Figure 1

The heavily pigmented infratemporal lesion on clinical examination was shown by slit-lamp biomicroscopy to represent a well-demarcated within the peripheral iris between 6 and 8 O'clock

Figure 2

The largest basal diameter was 4 mm × 2.5 mm, one of the most important features for estimating prognosis

Ultrasound biomicroscopy (UBM) revealed a solid mass deriving from the iris stroma without ciliary body involvement, suggesting a diagnosis of iris melanoma [Figure 3]. Fine-needle aspiration confirmed melanoma with a mix of the oval spindle and polyhedral epithelioid cells and inactivation of the BAP1 gene [Figures 4 and 5]. Both findings increased the likelihood of fatal metastasis and, thus, closer surveillance was indicated.[3]

Figure 3

Ultrasound biomicroscopy showed a solid mass with high/medium reflectivity and loss of the posterior iris plane. The mess appears to derive from the iris stroma without definite ciliary body involvement

Figure 4

Low-power microscopy of cellular aspirate demonstrating satisfactory yield of melanocytic cells

Figure 5

High-magnification microscopy showing spindle cell with a large nucleus and prominent nucleoli. Large melanosomes confirm spindle B-melanoma cells

The patient was treated with brachytherapy using a 12-mm diameter I-125 plaque implanted over the ciliary body and iris at the 7 o'clock meridian for 1 week for a total dose of 82 Gy.

UBM, 3 years later, demonstrated the success of the radiotherapy through the significantly reduced dimensions of the tumor [Figure 6]. Following radiotherapy, the patient developed a cataract, the most common complication occurring in 83% of cases.[4]

Figure 6

Ultrasound biomicroscopy, a 3-year postbrachytherapy, shows reduced tumor dimensions. Peripheral tumor location allowed for a treatment safety margin with a favorable visual prognosis

Discussion

Malignancies without BAP1 inactivation generally have a favorable prognosis due to their lower rates of visual morbidity and metastasis and 5-year mortality rate of 2–3%.[1] Hence, the management should reflect these auspicious outcomes. As the area of treatment involves a safety margin beyond the borders of the tumor, the effects of brachytherapy on visual prognosis are often dependent on the proximity of the tumor from the fundus. Given the peripheral placement of this patient's tumor, he had a favorable prognosis. The American Brachytherapy Society states an average follow-up of 53 months, with most eyes examined every 6 months and modulated based on likelihood for secondary complications, notably a shortened interval for posterior tumors due to the higher risk of radiation maculopathy and optic neuropathy.[5]

UBM has become crucial in the differentiation of uveal melanomas from benign growths, as lesions <3 mm cannot be reliably visualized by other imaging modalities.[6] As these cancers are often asymptomatic and indolent, careful monitoring is imperative to determine whether it is necessary to subject a patient to invasive biopsy or possible complications from surgical intervention or radiology. The advantages of UBM in anterior segment imaging include visualization of structures inaccessible to conventional methods such as the ciliary body and zonules, illustrating the degree of penetration of iris root and ciliary face in delineating solid masses from cystic lesions, and recording high-resolution cross-sectional images of diameter and thickness to document growth and determine malignancy.[7] The higher resolution afforded by UBM specifies the size, boundary, and elevation of the tumor that are important parameters in predicting metastasis and mortality. Additional findings consolidating the diagnosis include pronounced vasculature, hyphema, secondary cataract or glaucoma, and most importantly, documented growth.[3]

Clinicians should have a low threshold to refer or work up cases of pigmented eye uveal lesions due to their similarity in appearance of nevus and melanoma, and UBM acts as an effective modality to elucidate a diagnosis in these ambiguous cases. The differential diagnosis for uveal lesions includes iris nevus, iris cyst, essential iris atrophy, and foreign body. In differentiating iris melanoma from nevus on UBM, the common findings for melanoma include medium–high reflectivity, possible cavitation, and most importantly, a loss of the posterior iris plane.[7]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.