Multicavitary ciliary body melanoma presenting as a cyst.

Cyst-like cavities in uveal melanoma occur rarely and can simulate a benign intraocular cystic lesion resulting in delayed diagnosis and inappropriate management. Herein, we describe a 66-year-old Caucasian female who presented with a "cystic" ciliary body mass in the right eye oculus dexter (OD). Slit lamp examination OD showed anterior bulging of the iris temporally from an underlying pigmented ciliary body mass and transillumination disclosed slight shadow from the tumor. Ultrasound biomicroscopy (UBM) revealed multiple cyst-like cavities within a tumor, lined by "thick walls" of at least 200 μm and occupying 80% of the tumor volume. A clinical diagnosis of multi-cavitary ciliary body melanoma was suspected and partial lamellar sclero iridocyclectomy was performed. Histopathology confirmed the diagnosis of low-grade spindle melanoma of the ciliary body with multiple empty and fluid filled cyst-like cavities without epithelial lining. UBM is an important diagnostic tool in the differentiation of "thick walled" cavitary melanoma from "thin walled" benign pigment epithelial cyst.

Introduction

Ciliary body melanoma represents 6–15% of uveal melanoma.[12] This tumor usually presents as a solid mass, often pushing upon the iris, and appears acoustically hollow on ultrasonography. The presence of cyst-like cavities within solid melanoma can occur but is distinctly uncommon.[3-7] Ultrasonographically, this variant shows acoustically empty cavities within a relatively hollow uveal mass. In 1948, Kennedy described cavitary uveal melanoma, involving both the iris and ciliary body.[3] Since then, only a few cases have been reported.[4-7]

Most cavitary melanoma has been described in the ciliary body region. A retrospective study by Lois et al., described eight cases of cavitary ciliary body melanoma classified into multilocular (n = 5) and unilocular (n = 3) variants. Cavitation in uveal melanoma is rarely appreciated clinically, and best recognized by ultrasonography.[4] The challenge rests in the differentiation of thick-walled cavitation in melanoma from thin-walled benign iris pigment epithelial (IPE) cyst.[8] Ancillary studies with B-scan ultrasonography, ultrasound biomicroscopy (UBM), and anterior segment optical coherence tomography (AS-OCT) contribute to this differentiation.[489] Herein, we report a case of extensive cavitation within the ciliary body melanoma imaged with UBM and confirmed on histopathology.

Case Report

A 66-year-old Caucasian female was referred to the Ocular Oncology Service at Wills Eye Institute for a “cystic” ciliary body mass in the right eye (OD). On examination, visual acuity was 20/20 in both eyes. Anterior and posterior segment examination of the left eye oculus sinister (OS) was normal. Slit lamp evaluation of the right eye revealed anterior bulging of the iris temporally at 9:00 [Figure 1a]. On pupillary dilation, a pigmented ciliary body mass was noted, estimated to be 7 millimeters (mm) in base and 4 mm in thickness. Transillumination disclosed a shadow 7 mm in diameter, corresponding to the mass. On UBM, a multinodular ciliary body mass with solid tumor in the posterior and basal region was noted. Large areas of acoustically empty cavities were present and lined tissue walls measured 100–500 μm [Figure 1b]. The cavities occupied approximately 80% of the tumor volume. A clinical diagnosis of cavitary ciliary body melanoma OD was made and complete tumor resection with partial lamellar sclero iridocyclectomy was performed.

Figure 1

Multi-cavitary ciliary body melanoma in a 66-year-old Caucasian female. (a) Slit lamp photograph of the right eye showing temporal iris bulge suggestive of ciliary body mass. (b) Ultrasound biomicroscopy revealed a 4 mm thick ciliary body mass with solid tumor posteriorly as well as multiple acoustically empty cavities. (c) Gross pathology showed empty and sparse proteinaceous fluid-filled cavities following partial lamellar scleroiridocyclectomy. Scleral base is still attached. (d) Histopathology showed solid mass in the base and large cavities in the apex (H and E, ×15). (e) Composed of low-grade amelanotic spindle-shaped melanoma cells (H and E, ×20). (f) The tumor cells showed positive staining with melanoma marker microphthalmia transcription factor-2. Note that the empty cavities are lined by tumor cells and not epithelial cells (H and E, ×20)

Grossly, the sectioned tumor showed an irregular pigmented mass with numerous irregular cystic cavities [Figure 1c]. Histopathology disclosed a ciliary body tumor composed of low-grade amelanotic spindle-shaped melanoma cells with round or oval nuclei and containing finely dispersed chromatin [Figure 1d and e]. The tumor displayed extensive cavitary degeneration with multiple empty and proteinaceous fluid-filled cavities separated by trabeculae comprised of melanoma cells. There was no epithelial lining of the cavities. Only one mitotic figure was counted in 40 high power fields. Immunohistochemistry with melanoma markers indicated positivity with microphthalmia transcription factor-2, confirming the diagnosis of low-grade spindle melanoma of the ciliary body [Figure 1f]. At 3 years follow-up, there was no recurrence locally or systemically. Visual acuity was reduced to hand motions secondary to later retinal detachment, probably secondary to a retinal tear that was successfully treated.

Discussion

In a literature review of cavitary uveal melanoma by Zhang et al. in 2005, only 25 cases of cavitary uveal melanoma had been reported.[6] To our knowledge, only three other cases were subsequently reported.[6710] Of the total 28 documented cases of cavitary uveal melanoma, 25 (89%) were ciliary body/ciliochoroidal melanoma.[6710] Of these 25 cases of cavitary ciliary body/ciliochoroidal melanoma, ten (40%) were multi-cavitary melanoma. The cavities within the melanoma occupied a mean volume of 54% (range, 30-79%).[6] In our case, 80% of the tumor volume was replaced by cyst-like cavities.

Cyst-like cavities in malignant melanoma can be unilocular or multi-locular. It has been speculated that cyst-like cavities in melanoma appear due to accumulation of mucoproteinaceous substance[3] or serous exudate.[11] Other potential causes include hemorrhage or tumor necrosis secondary to an imbalance between blood supply and growth of the tumor mass.[3-5] Our case exhibited cyst-like cavities containing proteinaceous fluid, but did not show necrosis or hemorrhage.

Ciliary body melanoma can be misdiagnosed as a benign lesion when cyst-like cavities are found within the solid tumor. UBM and AS-OCT are useful in demonstrating single or multiple cavities, as well as tumor size, shape, and local extension.[8] These techniques are especially, helpful with small ciliary body melanoma, hidden behind the iris, where methods such as slit lamp examination, indirect ophthalmoscopy, and transillumination are usually inadequate to fully characterize the tumor. With regards to transillumination, a small ciliary body tumor shadow can blend with the normal shadow of the pars plicata, camouflaging the tumor shadow.[9] In our case, transillumination disclosed a 7 × 7 mm tumor shadow which was suggestive of a ciliary body tumor. However, a multi-cavitary tumor, replaced by large cyst-like cavities, could allow light transmission leading to a false impression of a benign cystic lesion.[6] AS-OCT can provide excellent resolution of the anterior margin of ciliary body tumors, while UBM is more favorable for visualization of the posterior margin and overall tumor configuration.[8]

The differential diagnosis of cavitary ciliary body melanoma include IPE cyst, ciliary body cyst, medulloepithelioma, cystic adenoma of pigmented ciliary epithelium, and ciliary body detachment.[1] The IPE cyst appears hollow on UBM with an extremely thin reflective wall consisting of an average thickness of 100 μm or less.[12] In contrast, cavitary ciliary body melanoma shows some degree of solid tumor base and apical thick-walled (200 μm to several millimeters) cavitary spaces.[4] The remainder of the differential conditions would be unlikely in this case due to tumor pigment (unlikely with ciliary body cyst), older age (unlikely for medulloepithelioma), and lack of ciliary body detachment on imaging.[61314] The main consideration in the differential diagnosis is solid adenoma of pigmented ciliary epithelium.[15] The true cysts in adenoma are often much smaller in diameter (cyst approximately 100 μm width or less) compared to cavitary melanoma (cavity approximately 500 μm width or greater).[1] In such cases, histopathology is required to establish the diagnosis of these simulating tumors.

In summary, we report a case of multi-cavitary ciliary body melanoma presenting as a cyst. Careful clinical examinations and typical UBM findings aid in the differentiation of cavitary ciliary body melanoma from other cystic and solid intraocular tumors.