Clinical features of midzonal iris pigment epithelial cysts: surprising findings revealed by ultrasound biomicroscopy.

Purpose: Midzonal iris pigment epithelial (IPE) cysts are typically asymptomatic but can pose a differential diagnostic challenge by mimicking ciliary body melanoma. We conducted a case series study of the clinical characteristics of these iris cysts, particularly their shapes and sizes and associated lesions revealed by ultrasound biomicroscopy (UBM).

Methods: Charts of patients with midzonal IPE cysts encountered by one or more of the authors were reviewed retrospectively. Pertinent demographic information and clinical data about these patients and their cysts were abstracted.

Results: 69 patients were identified. At initial diagnosis, patients ranged in age from 14.8 to 89.5 years (median: 66.0 years). Only one patient was < 30 years old at diagnosis. 38 patients (55.1%) were female. 74 eyes (39 right, 35 left) contained one or more clinically identified midzonal IPE cysts. The cysts involved the right eye alone in 34 (49.3%), the left eye alone in 30 (43.5%), and both eyes in 5 (7.2%) patients. The midzonal IPE cysts were located most often inferotemporally (51.4%) and second most often temporally (23.0%). UBM imaging had been performed on 44 of the 74 affected eyes. The median largest basal diameter of the midzonal IPE cysts evaluated by UBM was 4.5 mm (extremes: 1.5 to 13 mm), and the median height of these cysts was 1.5 mm (extremes: 0.6 to 6 mm). The largest lesion was a complete ring cyst. All 3 UBM-evaluated eyes that appeared by slit lamp biomicroscopy to have two or more distinct midzonal IPE cysts were shown by UBM to have a single sausage or kidney-bean shaped partial ring cyst with radial folds between the lobules and not separate multiple cysts. UBM imaging also identified peripheral IPE cysts in 32 of 44 evaluated eyes (72.7%).

Conclusions: Our case series confirmed previously reported findings regarding age at diagnosis and most common locations of midzonal IPE cysts. However, our UBM images revealed that at least some IPE cysts identified by slit lamp biomicroscopy as multifocal are partial ring cysts with radial folds in the cyst wall between lobules and not true independent multiple cysts.

Key messages: What is known Midzonal IPE cysts occur most often unilaterally and inferotemporally. Midzonal IPE cysts are frequently associated with peripheral IPE cysts. What is new UBM imaging of eyes with two-clinically detected IPE cysts showed that they were confluent as opposed to separate cysts. The median largest basal diameter of midzonal IPE cysts evaluated by UBM was 4.5 mm (extremes: 1.5 and 13 mm). The median height of midzonal IPE cysts evaluated by UBM was 1.5 mm (extremes: 0.6 and 6 mm).