Posterior Segment Tumors

15.2.1 Retinal Tumors

 Melanocytoma

Melanocytoma is most frequently observed at the optic disc more often in pigmented individuals, although these lesions may sometimes involve the choroid or iris. Unlike in choroidal nevus or choroidal melanoma, the typical optic disc melanocytoma infiltrates the retina, and retinal disorganization may be observed with spectral-domain OCT (SD-OCT).^13,​14

Although there have been no previously published reports on OCTA findings in optic disc melanocytoma, we have observed findings that are similar to established OCT findings. Vascular tortuosity with increased capillary volume density is observed at the superficial retinal layer ( ▶ Fig. 15.1). Both the deep retinal vascular layer and the choriocapillaris layer feature prominent signal void at the site of the lesion, which may arise from vascular signal blockage associated with the pigmented cells of the lesion. It is clear from OCTA that posterior melanocytomas are characterized by features that are distinct from both choroidal nevi and choroidal melanomas, where in these latter lesions there is usually no superficial retinal vascular alteration (see sections “Choroidal Nevus” and “Choroidal Melanoma”).

15.2.2 Retinal Pigment Epithelial Tumors

Tumors of the retinal pigment epithelium (RPE) are most commonly represented by the benign congenital hypertrophy of the retinal pigment epithelial lesion. However, retinal pigment epithelial adenomas, most commonly found in the retinal periphery and retinal pigment epithelial adenocarcinomas, also comprise this group of tumors.

 Congenital Hypertrophy of the Retinal Pigment Epithelium

Congenital hypertrophy of the retinal pigment epithelium (CHRPE) is a fairly common peripheral benign tumor of the RPE that has well-defined borders and may contain lacunae, or areas of depigmentation. These tumors rarely undergo malignant transformation. Occasionally, in young pigmented individuals with myopia, these benign tumors may simulate the appearance of an elevated choroidal mass and be mistaken for a choroidal melanoma.¹⁵

As most CHRPE lesions are located in the retinal periphery, they may be difficult to characterize by OCTA. We have found that the superficial and deep retinal layers are minimally altered. However, the choriocapillaris and choroidal layers clearly demonstrate the borders of the lesion and show signal void associated with the lesion with greater penetration to the choroid ( ▶ Fig. 15.2).

15.2.3 Choroidal Tumors

Determining distinguishing features of macular choroidal lesions on OCTA has been somewhat challenging because OCTA may not be the ideal tool for evaluating choroidal vasculature, and rarely do the superficial retinal vessels overlying a choroidal mass display any clinically abnormal features. Furthermore, lesions that are elevated and greater than 2.0 mm result in areas of flow-void and present challenges with optical capture.

 Choroidal Nevus

Choroidal nevi are the most common intraocular tumors, with a higher prevalence among Caucasians (0.2 to 20%) compared to other races.^14,​16 They do not often cause visual symptoms, and on examination are typically pigmented with smooth margins and may have overlying drusen. Although choroidal nevi are benign, it has been estimated that 1 in 8,845 choroidal nevi undergoes transformation to choroidal melanoma.¹⁴ As such, careful evaluation and follow-up is advised, particularly in elevated choroidal nevi.

OCT has been used to differentiate nevi from melanomas, and also to identify features that predict transformation. Overlying drusen are found in 40% of choroidal nevi, and manifest as small, dome-shaped elevations at the level of the RPE/Bruch’s membrane.¹⁴ Other common imaging features on OCT include choroidal shadowing deep to the nevus, choriocapillaris thinning overlying the nevus, RPE atrophy or loss, RPE modularity, photoreceptor loss, ellipsoid zone irregularity or loss, external limiting membrane irregularity, outer nuclear and outer plexiform layer irregularity, inner nuclear layer irregularity, and subretinal fluid.¹⁶

OCT has a higher sensitivity than clinical examination in the detection and characterization of overlying intraretinal edema, subretinal fluid, retinal atrophy, and RPE detachment. These features are significant, and may influence foveal vision in macular nevi, as well as represent features of malignant transformation.¹⁴

Valverde-Megías et al reported on the OCTA findings of central macular thickness, superficial and deep foveal avascular zone, and capillary vascular density of the macula in 70 eyes harboring a nevus outside the macula (average thickness: 1.38 mm; range: 0–2.4 mm) compared to the macular findings in the contralateral eye. There were no significant differences in these parameters of the macula between the normal and the nevus eye.¹⁷

The OCTA features through a flat choroidal nevus are depicted in ▶ Fig. 15.3 and ▶ Fig. 15.4, and an elevated choroidal nevus in ▶ Fig. 15.5 and ▶ Fig. 15.6. As previously reported, choroidal nevi do not generally result in alteration of the overlying retinal vasculature. However, as the thickness of the lesion increases, the elevation through the deep retinal layers may manifest as signal void. Given the origin of these lesions in the choroidal layer, choroidal nevi demonstrate most of the OCTA alterations in the choriocapillaris and deep choroidal layers. At the more superficial choriocapillaris, signal void is observed at the site of the choroidal nevus. In the deeper choroidal layer, hyper-reflectivity may be observed. The etiology of the hyper-reflectivity is not clearly understood, but may represent the density of the choroidal pigment, which comprises these lesions.

 Choroidal Melanoma

Uveal melanoma is the most common primary intraocular malignancy in adults, and 90% develop in the choroid.¹⁴ The focus of this section will be on posterior uveal melanoma, otherwise described as choroidal melanoma. Clinical examination reveals an elevated choroidal mass sometimes with serous retinal detachment. Multimodal imaging identifies features of activity and leakage.

Relatively little is known about the OCTA findings associated with choroidal melanoma. Previous evaluation of macular OCTA findings, regardless of location of the actual tumor, has revealed an enlargement of the deep foveal avascular zone and a reduction in superficial and deep capillary vascular density. The extent of these vascular alterations were dependent on tumor size, suggesting that parafoveal microvascular ischemia was caused by the melanomas themselves.^17,​18

OCTA through the melanoma itself may be most useful in the evaluation of small uveal melanoma (i.e., <2.0 mm) as there is less choroidal elevation to alter the superficial and deep retinal layers. Examples of small choroidal melanoma and their corresponding OCTA images are demonstrated in ▶ Fig. 15.7 and ▶ Fig. 15.8. In tumors of thickness less than 2.0 mm, there is often no significant vascular alteration in the superficial retinal layer. The deep retinal layer may demonstrate mild to moderate loss of vessels overlying the tumor. The choroid layer may reveal mostly loss of signal in the area of the melanoma.

 Choroidal Metastasis

Choroidal metastatic tumors are the most common intraocular neoplasm of adults. Without a known medical history of cancer, however, making the diagnosis of metastatic tumor may be challenging. The vast majority of ocular metastatic tumors develop in the choroid perhaps because of its rich vascular supply.^1,​14 Well-described clinical features, such as yellow coloration, irregular borders, multiple lesions, bilateral involvement, and irregular appearance on ultrasonography may assist in making the correct clinical diagnosis. Most patients have a prior history of systemic cancer: breast cancer is the most common type to metastasize, accounting for 48 to 53% of cases.¹⁴ This is followed by prostate cancer, cutaneous melanoma, and lung cancer.^1,​16 Among the 34% of patients who do not have a history of cancer, the lung is the most common primary source after evaluation.¹⁴

There have been no previous reports of OCTA findings regarding choroidal metastatic tumors. Findings may be somewhat similar to choroidal melanoma, a sometimes-similar appearing malignant neoplasm of the choroid. As such, we have found choroidal metastatic tumors to have minimal alteration of the superficial retinal layer, mild alteration of the deep retinal layer, and signal void in the choroidal layer ( ▶ Fig. 15.9).

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