Giant leiomyoma of the ciliary body.

Leiomyoma is a rare intraocular tumor that arises from uveal smooth muscle. Herein, we report a large leiomyoma that occupied nearly 50% of the globe, closely resembling melanoma. A 40-year-old female presented with a 17 × 15 × 11 mm amelanotic ciliochoroidal mass causing visual defect in her right eye (OD). Based on transillumination features of tumor shadow and ultrasonographic features of acoustically solid mass, there was low clinical suspicion for leiomyoma or schwannoma, and a preliminary diagnosis of ciliochoroidal melanoma was rendered. Following enucleation, histopathology revealed a paucicellular tumor comprised of spindle cells, with positive immunostaining for smooth muscle actin and negative stains for melanoma markers (S-100 protein, HMB45, and MITF-2). These features were consistent with ciliochoroidal leiomyoma. Benign uveal leiomyoma can achieve an unusually large size and block light transmission on transillumination, features that simulate malignant melanoma.

Introduction

Intraocular leiomyoma is an extremely rare tumor, with a tendency to manifest in young adult females.[1] This benign tumor can arise from smooth muscle tissue in the iris or ciliary body or from heterotopic smooth muscle in the choroid. Additionally, this tumor can arise from the smooth muscle surrounding blood vessels within the eye.[123] The term “mesectodermal leiomyoma” is applied to those tumors arising from neural crest derived intraocular smooth muscle, whereas “mesodermal leiomyoma” refers to those tumors derived from smooth muscle surrounding vessels.[23]

Uveal leiomyoma can closely simulate malignant amelanotic uveal melanoma from clinical and imaging perspectives. Both can appear as a dome-shaped, non-pigmented, smooth-surfaced, solid vascular mass originating in the uvea. Both can extend through the wall of the eye and become extra scleral.[4] However, there are some subtle differentiating features found on transillumination, in which leiomyoma usually transmits light and melanoma blocks light. Other differentiating features by ultrasonography show leiomyoma as a dome-shaped mass and melanoma as either dome- or mushroom-shaped. Furthermore, there is a subtle feature on ultrasonography in which some leiomyomas appear in a suprauveal location, whereas melanoma is within the uveal stroma.[2] Based on the largest published series, leiomyoma is detected at mean 7 mm thickness,[2] whereas melanoma is detected at mean 5.5 mm thickness.[5] Herein, we describe a large ciliochoroidal leiomyoma with melanoma imaging features in that it blocked transillumination.

Case Report

A 40-year-old Caucasian woman noted a visual field defect and floaters in her right eye (OD) for two months. On examination, best-corrected visual acuity was 20/20 in each eye (OU). Intraocular pressure was normal OU. Ocular examination OS was normal. Fundus examination OD revealed a large amelanotic ciliochoroidal mass occupying nearly one-half of the globe and with serous retinal detachment, sparing the fovea. The mass measured 17 × 15 mm in basal dimension. On transillumination, the mass cast a relatively dark shadow consistent with melanoma. B-Scan ultrasonography confirmed an acoustically solid tumor of 11 mm thickness. [Figure 1a] Fluorescein angiography disclosed intrinsic vascularity and “double circulation” pattern, predominantly in the early venous phase. Based on these findings, a preliminary diagnosis of large ciliochoroidal melanoma was rendered and enucleation was performed.

Figure 1

Giant mushroom-shaped leiomyoma of the ciliary body. (a) Ultrasonography demonstrating solid, dome-shaped ciliary body mass. (b) Transillumination of the globe showing the intraocular tumor casting a relative shadow (white dotted line). (c) Gross pathology showing amelanotic tumor in the suprauveal space (d) Histopathology confirming suprauveal tumor location without stromal invasion (Hematoxylin-Eosin stain, original magnification ×10) (e) Microscopy demonstrating the paucicellular tumor composed of bland spindle cells without mitotic activity. (Hematoxylin-Eosin stain, original magnification ×40) (f) Immunohistochemistry showing positive immunoreactivity for smooth muscle actin (SMA), with ciliary muscle serving as a positive control (SMA, original magnification ×40)

The enucleated globe showed a relatively dark shadow on transillumination. [Figure 1b] On gross examination, the amelanotic tumor appeared external to the pigmented uvea [Figure 1c] and histopathology confirmed suprauveal location and no infiltration of the uveal stroma. The paucicellular tumor consisted of interweaving fascicles of bland spindle cells with eosinophilic cytoplasm and elongated nuclei. There were no mitotic figures. [Figures 1d and 1e] Immunohistochemistry disclosed a positive stain for smooth muscle antigen (SMA, muscle tissue marker) [Figure 1f], and the tumor was non-reactive for melanocytic markers including S-100 protein, human melanoma black 45 (HMB45), and microphthalmia transcription factor 2 (MITF-2). These features were consistent with suprauveal ciliochoroidal leiomyoma.

Discussion

Uveal leiomyoma shows characteristic clinical features of an orange-colored, dome-shaped mass, usually in the ciliary body with prominent intrinsic vascularity, generally in a young adult female.[12] One distinguishing feature is its prominent transmission of light on transillumination, unlike other solid intraocular tumors.[12] Despite these findings, uveal leiomyoma can mimic amelanotic melanoma, schwannoma, neurofibroma, lymphoma, and metastatic tumor.[26]

Uveal leiomyoma can exhibit slow growth and extend into the anterior chamber,[789] and produce ocular complications such as subluxation of the lens, glaucoma, and retinal detachment.[12] Leiomyoma can also extend through the sclera into the orbit.[6] Despite the benign cytology, therapeutic intervention is usually necessary. In our patient, the tumor was large (11 mm thickness) and producing retinal detachment and visual field defect, necessitating enucleation.

With regard to imaging, uveal leiomyoma classically exhibits enhanced transillumination with brighter transmission of light through the tumor compared to the surrounding uvea.[12] This could be attributed to absence of pigmented cells at the site of the solid non-pigmented tumor, suprauveal location of the non-pigmented mass, abundant connective tissue, and paucicellularity of the tumor. In contrast to leiomyoma imaging, transillumination shows blockage of light for most other solid tumors including marked shadow for heavily pigmented melanoma, moderate shadow for non-pigmented melanoma, and often a light shadow for metastasis. However, in this leiomyoma, a comparatively dark shadow was cast on transillumination, opposite to what was anticipated, perhaps related to the large tumor size.

High-quality B-scan ultrasonography is another imaging modality to differentiate leiomyoma from melanoma. Leiomyoma assumes a dome shape on ultrasonography, similar to melanoma. Leiomyoma can occasionally be identified in a suprauveal location on ultrasonography, extrinsic to the choroid or ciliary body.[5] In our case, suprauveal tumor location was not evident on ultrasonography but was confirmed on histopathology.

On MRI imaging, there are no differentiating features of leiomyoma versus schwannoma versus malignant melanoma. All are hyperintense on T1-weighted images and hypointense on T2-weighted images. All show contrast enhancement.

The management of leiomyoma depends on tumor size and location. Small leiomyomas, if the diagnosis is strongly suggested, can be cautiously observed. This is rarely the case since amelanotic melanoma cannot be excluded in most instances. If the tumor involves 3-4 clock hours of the iris/ciliary body, then the tumor can be removed by partial iridectomy or partial lamellar sclerouvectomy can be employed.[110] If suprauveal, leiomyoma can be removed from the globe without incision into the uveal tissue.[11] Larger tumors are often managed with enucleation or radiotherapy, with erroneous diagnosis of melanoma. Outcomes following radiotherapy are not known.

In summary, uveal leiomyoma can closely clinically simulate malignant melanoma. Despite characteristic clinical features for each tumor, there is considerable overlap of findings. Fine needle aspiration biopsy could prove useful in differentiation of these conditions.[12] Definitive diagnosis is often achieved with histopathology and immunohistochemistry as leiomyoma cells show positive reaction to muscle-specific actin and smooth muscle antigen and a negative reaction to melanoma-specific antigens S-100 protein, HMB45, and MITF-2.[113]