Case Report: Optic Disc Melanocytoma with PHOMS—Minimum Intensity Projection Image

Introduction

Optic disc melanocytoma with peripapillary hyperreflective ovoid mass-like structures (PHOMS) is rare. This study reports a case of the characteristics of multimodal imaging and Minimum intensity projection (Min-IP) images.

Case Presentation

A 25-year-old male patient was referred to our hospital due to the presence of a dark pigmented tumor located in the optic disc area of his left eye, as observed during physical examination. The patients’ medical and family histories were unremarkable. The right eye was essentially normal. The best corrected visual acuity (BCVA) was 1.0 (decimal) in both eyes, and the intraocular pressure measured 17 mmHg in the right eye and 18 mmHg in the left eye, accompanied by normal pupillary reactions bilaterally. The slit lamp biomicroscopic examination revealed unremarkable anterior segments of both eyes.

The lesion of left eye was documented on multimodal imaging. The color fundus photograph (CFP) showed a black to dark brown slightly elevated mass lesion in inferior quadrant of the left optic disc with feathery margins and obscured superonasal quadrant disc margin (Clarus 500, Carl Zeiss Meditec, Inc). B-scan ultrasonography of the left eye revealed a hyperechoic, small dome-shaped lesion with dimensions of 2.83 mm in largest basal diameter and 1.11 mm in thickness (SW-2100, Tianjin, China), as confirmed by imaging analysis. Fluorescein angiography (FA) revealed hyperfluorescent staining of the peripapillary hyperreflective ovoid mass-like structures (PHOMS) located at the superonasal rim of the left optic disc, along with diffuse blocked hypofluorescence observed in all phases within the region covered by the pigmented lesion of optic disc melanocytoma (ODMC), without any indication of late phase hyperfluorescence (VISUCAM524, Digital fundus camera, Germany). Fundus autofluorescence (FAF) revealed a totally hypofluorescent mass with sharply demarcated, feathery edges (Panoramic ophthalmoscope, Daytona P200T). (Figure 1)

Figure 1 CFP showing a optic disc melanocytoma with black to dark brown slightly elevated mass lesion of the left optic disc. (A) B-scan ultrasonography of the left eye showing a hyperechoic small dome shaped lesion. (B) FAF revealed a totally hypofluorescent mass. (C) FA showed the hyperfluorescence staining of PHOMS at the superonasal rim of the left optic disc and diffuse blocked hypofluerescence in ODMC (D).

SD-OCT (spectral-domain optical coherence tomography) and OCTA (optical coherence tomography angiography) with Minimum intensity projection (Min-IP) (Cirrus HD-OCT 5000, Germany) were performed over the tumor and its surrounding areas. Min-IP is a novel algorithm of an en-face visualization of the retina that identifies and displays the minimum optical intensity found between the internal limiting membrane and retinal pigment epithelium. SD-OCT showed an elevated tumor mass arising from the left optic disc with increased reflectivity at its anterior margins and a dense optically empty space at its posterior margin due to tumor shadowing.

PHOMS appeared ovoid in shape on B-scan (cross-sectional) OCT image and appeared peripapillary hyperreflective bright areas on en-face Min-IP image corresponding to PHOMS on B-scan OCT image. PHOMS showed that blood flow signal of the deep capillary plexus(DCP) was decreased on OCTA. (Figure 2)

Figure 2 SD-OCT images of ODMC (A) and PHOMS (yellow arrow, (B). OCTA images showing superficial capillary plexus (C) and the blood flow signal of the deep capillary plexus was decreased in PHOMS (yellow arrow, (D). PHOMS showing peripapillary hyperreflective bright areas on en-face Min-IP image corresponding to B-scan OCT image (E, F, G and H, yellow arrow).

A diagnosis of optic disc melanocytoma with PHOMS was established based on its characteristic location and clinical features, prompting the patient to be advised for regular follow-up.

Discussion

Optic Disc Melanocytoma is an infrequent, benign, unilateral primary tumor of the optic disc characterized by its highly pigmented nature and distinct leafy margins.¹ The occurrence of optic disc melanocytoma with PHOMS is exceptionally uncommon.

The SD-OCT characteristics of ODMC have been described as a dome-shaped lesion exhibiting hyper-reflectivity on its anterior surface and dense posterior shadowing, resembling an optical cavity.² OCTA offers a noninvasive, safe, and efficient technique for assessing various neoplasms, including the growth and vascularity in ODMC. Moreover, OCTA has the potential to enhance the evaluation of vascular abnormalities in tumors while demonstrating that melanin’s impact on OCTA beam penetration is not statistically significant.³ Fundus autofluorescence imaging serves as a non-invasive adjunctive tool for distinguishing optic disc melanocytoma from juxtapapillary choroidal nevus and juxtapapillary uveal melanoma.⁴

Differential diagnosis of the peripapillary lesion encompassed optic disc melanocytoma with secondary CNV, choroidal melanoma, choroidal nevus, congenital hypertrophy of the retinal pigmented epithelium (CHRPE), and combined hamartoma of retina and retinal pigmented epithelium (RPE). Ultrasound features such as a thickness less than 2 mm and base smaller than 5 mm, high internal reflectivity, and absence of acoustic hollowness (a characteristic feature of melanoma), in conjunction with its juxtapapillary location and the patient’s age, indicated a benign pigmented lesion.⁵

The widespread adoption of SD-OCT and EDI-OCT (enhanced depth imaging-optical coherence tomography) has resulted in the recognition of PHOMS as a prevalent neuro-ophthalmological finding using OCT technology.⁶ It was postulated that PHOMS could potentially be attributed to a lateral herniation of distended retinal ganglion cell axons into the peripapillary region, firmly ensconced between the peripapillary nerve fiber layer and Bruch’s membrane, thereby giving rise to a torus or doughnut-shaped structure encircling the disc margin.⁷ PHOMS refers to a condition characterized by the lateral bulging herniation of distended axons into the peripapillary region above Bruch’s membrane opening. It should be noted that PHOMS is not simply synonymous with buried optic disc drusen (ODD), as previously described. The frequent coexistence of PHOMS with ODD, papilloedema, anterior ischaemic optic neuropathy, tilted optic disc syndrome, inflammatory demyelinating disorders, and other diseases associated with axoplasmic stasis offers valuable insights into its underlying pathophysiology.⁸

The present study examines the role of en-face Min-IP image in investigating the existing literature on the correlation between PHOMS and common neuro-ophthalmic conditions. Min-IP OCT is an innovative algorithm that identifies and presents the minimum optical intensity observed between the internal limiting membrane and retinal pigment epithelium. Initially designed to generate an en face fundus image, this software highlights fluid as dark regions. In a healthy retina, the outer nuclear layer exhibits the minimum intensity signal.⁹ In this study, peripapillary hyperreflective bright areas corresponding to PHOMS on B-scan OCT image were observed as evident on en-face Min-IP image.

Furthermore, despite its benign nature, it harbors the potential for malignancy. Therefore, regular annual assessments are imperative to identify any alterations in the texture, dimensions, and morphological characteristics of the ODMC.¹⁰ On B-scan ultrasonography, Gologorsky et al utilized high-resolution B-scan imaging to evaluate benign lesions for potential signs of malignant transformation, such as an increase in size, vascularity, and the development of a nodular appearance.² The multimodal imaging and en face Min-IP image possess significant clinical diagnostic value.