Distinguishing midzonal iris pigment epithelial cyst from adenoma and ciliary body melanoma.

A 49-year old male with corrected visual acuity of 20/25 OD and 20/20 OS was found to have an asymptomatic dark iris mass OD with suspicion for ciliary body melanoma. Predilation slit-lamp biomicroscopy revealed a well-circumscribed brown round mass arising posterior to the iris, presumably from the ciliary body; however, postdilation demonstrated an extended fusiform mass of the iris pigment epithelium (IPE). By anterior segment imaging, the well-circumscribed IPE mass was cystic and measured 1440 microns in thickness peripherally predilation and 300 microns in thickness postdilation. There was no solid IPE or ciliary body component. A diagnosis of midzonal IPE cyst was rendered and observation advised. Clinical features and anterior segment imaging can assist in differentiation of midzonal IPE cyst from adenoma and ciliary body melanoma. The diagnostic methodology described in this paper can be used by ophthalmologists to promptly rule out underlying melanoma.

Introduction

Iris pigment epithelial (IPE) cysts are thin-walled, epithelium-lined, fluid-filled spaces that arise from the posterior layer of the iris.[12] Most IPE cysts are benign and unilateral.[12] The challenge comes with differentiating IPE cyst from other solid iris, IPE, and ciliary body tumors.[13] In particular, midzonal IPE cyst can simulate IPE adenoma/adenocarcinoma and ciliary body melanoma.[13] To distinguish these lesions, slit-lamp biomicroscopy, anterior segment optical coherence tomography (AS-OCT), ultrasound biomicroscopy (UBM), and transillumination should be utilized.

Case Report

A 49-year-old male was referred to the Wills Eye Ocular Oncology Service for evaluation of a dark iris tumor in the right eye.

On examination, corrected visual acuity was 20/25 OD and 20/20 OS. Predilation slit-lamp biomicroscopy OD [Figure 1] revealed a circumscribed brown mass arising on the posterior surface of the iris from 6:30 to 9:00 meridians. The smooth-surfaced mass caused no ectropion or corectopia and demonstrated no feeder or intrinsic blood vessels as often observed with melanoma. Postdilation slit-lamp biomicroscopy OD [Figure 2] revealed a more prominent fusiform brown mass extending from 3:00 to 9:00 inferiorly, with a notably distended portion between 6:30 and 9:00 meridians. Predilation AS-OCT OD [Figure 3] showed a well-circumscribed cystic mass on the posterior surface of the iris with normal overlying iris stroma measuring a thickness of 1440 microns peripherally and 650 microns in the pupillary aperture. Postdilation UBM OD [Figure 4] showed an elongated cystic mass with a thinner measurement of 300 microns peripherally and 720 microns in the pupillary aperture. The UBM findings OS revealed three peripheral IPE cysts at 3:00, 6:00, and 9:00, without change upon dilation. There was no tumor seeding or evidence of malignancy.

Figure 1

Predilation slit-lamp photograph of the right eye (OD) shows a hidden brown round lesion on the posterior surface of the iris from 6:30 to 9:00 pupillary margin

Figure 2

The postdilation counterpart better illustrates a brown fusiform lesion with smooth contour from 3:00 to 9:00. This lesion was notably distended between 6:30 and 9:00

Figure 3

Before dilation, a well-circumscribed cystic mass showed thickness of 1440 microns peripherally on anterior segment optical coherence tomography OD

Figure 4

In contrast, after dilation, the elongated cystic mass showed thickness of 300 microns peripherally on ultrasound biomicroscopy OD

The patient was diagnosed with large midzonal IPE cyst OD and three small peripheral IPE cysts OS. Management with observation was advised.

Discussion

Midzonal IPE cysts simulate other tumors such as IPE adenoma/adenocarcinoma and ciliary body melanoma, which display a brown-black color, round configuration, and appearance following dilation.[14] The midzonal IPE cyst and even IPE adenoma can be quiescent and typically are managed with observation.[14] On the rare occasion when the midzonal cyst obstructs the visual axis or causes angle closure, fine needle aspiration for cyst deflation can be employed.[2] IPE adenoma/adenocarcinoma can demonstrate growth, causing cataract and lens subluxation and require surgical resection.[4] Finally, ciliary body melanoma is a serious malignancy that often demonstrates overlying episcleral sentinel blood vessels, lens subluxation, transillumination shadow, solid mass with intrinsic vascular pulsations on ultrasonography, and occasional retinal detachment.[25] Ciliary body melanoma requires prompt treatment with plaque radiotherapy, surgical resection, or enucleation as this tumor carries prominent risk (33%) for metastasis at 10 years from diagnosis.[2]

Imaging of IPE cysts with AS-OCT and UBM permits a thorough examination of cystic versus solid mass. On imaging, midzonal IPE cyst shows a very thin wall with absent reflectivity within the cyst. In contrast, adenoma/adenocarcinoma is centrally dense and arises from the epithelial structures, while ciliary body melanoma is centrally dense, often with vascular pulsations, and arises from the uveal structures.[25]

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.