Three-dimensional spectral-domain optical coherence tomography of melanocytoma of the optic nerve head

Introduction

Melanocytoma of the optic nerve head is a benign melanocytic lesion that usually occurs in the inferotemporal area of the optic nerve head. The uveal melanocytes emanating from the neural crest during embryogenesis are believed to be the cells of origin. These cells are present in the lamina choroidalis, the portion of the optic nerve adjacent to the choroid. The tumor is typically unilateral and stationary and rarely undergoes a malignant transformation. The condition is usually asymptomatic except when the tumor undergoes extensive necrosis or malignant transformation or is associated with the choroidal neovascular membrane [1]. Shields et al. [2] described that melanocytoma, although benign, has the capacity to cause significant visual morbidity. They reported that at 10 and 20 years, respectively 18% and 33% will lose two or more lines of vision by Kaplan–Meier estimates.

Spectral-domain optical coherence tomography (OCT) is increasingly being used in various retinal disorders because it has high-resolution imaging capabilities. This system allows a faster acquisition time than the conventional time-domain OCT, thus allowing a larger number of images to be acquired resulting in scans of higher resolution and three-dimensional analysis [3].

Case report

A 53-year-old male presented at our tertiary care center with the complaints of gradual, progressive, painless diminution of vision for 3 months, not associated with any other ocular or systemic complaints. His best-corrected visual acuity in the right eye was 20/20 and counting finger in the left eye. Slit lamp biomicroscopy of the anterior segment, in both eyes, was unremarkable, without melanocytosis of the conjunctiva. Fundus examination of the left eye revealed a dark, elevated lesion at and around the optic nerve with an extension to the nasal and inferior chorioretina (Fig. 1). Fluorescein angiography showed a typical hypofluorescence in the area of the elevated mass.

Fig. 1.

Color fundus photograph showing melanocytoma of the optic nerve head

Spectral-domain OCT (Carl Zeiss Meditec Inc., CA, USA), optic disk cube 200 × 200 advanced visualization displayed a dome-shaped lesion with a gradual slope at the tumor margin. Areas of irregular hyper-reflectivity were observed in the area of melanocytoma (Fig. 2a). Retinal pigment epithelium (RPE) was found to be extending within the melanocytoma in the horizontal scan as well as on 3D analysis (Fig. 2a, b). This is in contrast to the abrupt discontinuation of the retinal pigment epithelium in the normal right eye (Fig. 3). Dense posterior shadowing obscured all optical details of the optic nerve (Figs. 2 and 4). Retinal nerve fiber layer (RNFL), characterized by hyper-reflective signals, was observed to continue with the melanoma mass (Fig. 2). On 3D analysis of macular cube 512 × 128, internal limiting membrane–retinal pigment epithelium (ILM-RPE) map revealed mean foveal thickness of 208 μ (Fig. 5). Macular thickness in the superior quadrant was 291 μ whereas macular thickness in the nasal quadrant (adjacent to disk) was 295 μ. The ILM and RPE maps were unremarkable.

Fig. 2.

a Spectral-domain OCT optic disk cube 200 × 200 advanced visualization shows areas of irregular hyper-reflectivity in the area of melanocytoma. Retinal pigment epithelium is found to be extending within the melanocytoma. b Three-dimensional spectral-domain OCT shows areas of irregular hyper-reflectivity in the area of melanocytoma. Retinal pigment epithelium is found to be extending within the melanocytoma

Fig. 3.

Spectral-domain OCT optic disk cube 200 × 200 advanced visualization display of the normal eye abrupt discontinuation of the retinal pigment epithelium

Fig. 4.

Three-dimensional spectral-domain OCT in z-axis shows dense posterior shadowing, obscuring all optical details of the optic nerve

Fig. 5.

Three-dimensional spectral-domain OCT ILM-RPE map (false color map) reveals increased macular thickness

Optic disk cube 200 × 200 RNFL analysis of the right eye showed a normal thickness of optic nerve head with average being 84 μ. The superior and inferior rim showed 98 and 118 μ, respectively, which was normal when compared with the normative database. In the left eye, the average thickness of the optic nerve head was 69 μ, showing markedly increased thickness in the inferonasal part (200 μ) due to the underlying mass. Superotemporal and inferotemporal areas of the optic nerve head showed thinning. This thinning was observed to be more from one to five o’clock position (probability of <1% of the normative database) secondary to stretching, revealed as generalized thinning on OCT (Fig. 6). Extracted RNFL circle image of the left eye also showed tumor mass with optical shadowing.

Fig. 6.

Spectral-domain OCT optic disk cube 200 × 200 retinal nerve fiber layer thickness analysis

Discussion

Melanocytoma of the optic nerve head is a rare, distinctive, deeply pigmented benign tumor, frequently (in 54% of the cases) involving the adjacent retina and choroid [4–7]. Spectral-domain OCT revealed novel findings. Retinal pigment epithelium was found to extend within the melanocytoma. This is in contrast to the abrupt discontinuation of the retinal pigment epithelium normally at the disk. Retinal nerve fiber layer was also observed to continue with the melanoma mass. The ILM-RPE map topographically depicted the associated macular edema.

Dense posterior shadowing obscured all the optical details of the optic nerve. This empty space behind the high reflectance is due to the blockage of the light transmission through the deeply pigmented tumor [5, 8]. The RNFL showed significant axonal fiber loss resulting in severe visual loss. This pathological thinning is the result of chronic compression of the optic nerve and secondary stretching of the overlying retina.

Melanocytoma of the optic nerve head has unique optical coherence tomography characteristics, especially with the new generation of higher resolution instruments. This may help evaluate, follow, and determine the prognosis for these patients.