Multimodal imaging of choroidal nodules in neurofibromatosis type-1.

Choroidal nodules in neurofibromatosis type-1 are common and are best imaged with near-infrared reflectance (NIR) imaging. The authors describe swept-source optical coherence tomography angiography (SSOCTA) of choroidal nodules. These nodules are seen as hyperflow areas on SSOCTA and correlate well to bright patches on NIR imaging. The utility of multicolor scanning laser imaging in detecting these abnormalities is also described.

Choroidal nodules in the setting of neurofibromatosis type-1 (NF-1), also known as choroidal neurofibromatosis, occur commonly and can be seen in up to 82% of the NF-1 patients.[1] These nodules are characterized by ovoid bodies consisting of proliferating neoplastic Schwann cells that are arranged in concentric rings around axons.[2] These choroidal nodules are poorly visible on clinical examination and conventional color photographs. Near-infrared reflectance (NIR) imaging is the best imaging modality to visualize these nodules, which are seen as multiple bright patches on this imaging modality.[3] The high prevalence of these nodules in patients with NF-1 has prompted the researchers to recommend it as new diagnostic criteria for the detection of NF-1.[1]

Swept-source optical coherence tomography (SS-OCT) uses a longer wavelength (1050 nm) and allows simultaneous imaging of vitreous, retina, and choroid due to better penetration. OCT angiography (OCTA) is a recently introduced noninvasive tool for rapid assessment of retinal vasculature and can provide us with depth-resolved detection of abnormalities in the retinal microvasculature. OCTA with swept-source platform can provide additional information on choroidal vasculature as well. We describe SS-OCTA features of choroidal nodules in NF-1 along with multimodal imaging. This is the first report of OCTA of choroidal neurofibromatosis to the best of our knowledge.

Case Report

A 22-year-old male with NF-1 presented with upper lid mass since many years. Best-corrected visual acuity was 20/20 in both the eyes. The left eye upper lid showed a plexiform neurofibroma. Intraocular pressure was 14 mmHg in both the eyes. Anterior segment examination was unremarkable in both eyes apart from the presence of Lisch nodules. Dilated fundus examination of the right eye was apparently normal [Fig. 1]. A multicolor scanning laser image (Spectralis, Heidelberg Inc.) showed multiple scattered red lesions at the posterior pole and around the optic disc [Fig. 2a]. These red lesions on multicolor images corroborated well with the bright patches on the NIR image [Fig. 2b]. SS-OCT (Triton, Topcon Inc.,) B-scan was obtained through the fovea and the choroidal lesion [indicated by blue arrow in Fig. 2a]. The choroidal lesion [arrowheads in Fig. 2a and c] was seen to be present in the outer choroid and choriocapillaris appeared thinned out.

Figure 1

Color fundus photograph of the right eye of a patient with neurofibromatosis type-1 appears normal

Figure 2

Multicolor scanning laser image (a) of the right eye showing choroidal nodules as red lesions, which corroborate well with bright patches on near-infrared reflectance imaging (b). Swept-source optical coherence tomography B-scan (c) through the fovea (blue arrow) shows choroidal nodules in the deeper choroid (arrow heads). Green arrow shows the retinal corkscrew vessels

A 9 mm × 9 mm area around the fovea was imaged using SS-OCTA (Triton, Topcon Inc.) in the right eye. The automated OCTA image obtained at the level of superficial and deep capillary plexus revealed a retinal “cork-screw” vessel temporal to the fovea [Fig. 3a, blue arrow and b]. OCTA imaging at the level of choriocapillaris showed low flow (dark) areas corresponding to the nodules [arrows, Fig. 3c]. OCTA image of outer choroid revealed hyperflow areas corresponding to the bright patches on NIR imaging [Fig. 3d]. The bright patches seen on NIR imaging corroborated well with the hyperflow areas on the OCTA of deep choroid [Fig. 4]. Similar findings were present in the left eye. The patient was apprised of the situation and was referred to oculoplasty services for the management of plexiform neurofibroma of the left upper lid.

Figure 3

Swept-source optical coherence tomography angiography (of the superficial (a) and deep retinal plexus (b) shows retinal cork-screw vessels (blue arrow). Optical coherence tomography angiography of choriocapillaris shows low flow areas (blue arrows, c). Optical coherence tomography angiography of deep choroid shows hyperflow bright areas corresponding to the choroidal nodules (d)

Figure 4

Bright patches on near-infrared reflectance image (a) corroborate well with hyperflow areas on optical coherence tomography angiography of deep choroid (b) the segmentation of which is seen in the B scan (c)

Discussion

This report highlights multimodal imaging features of choroidal neurofibromatosis. While it is known that these nodules are visualized best on NIR imaging, this is the first report to show that multicolor scanning laser imaging also provides excellent visualization of choroidal abnormalities in NF-1. Multicolor imaging utilizes a scanning laser ophthalmoscope for obtaining images using infrared, green, and blue lasers simultaneously. Since various tissues reflect different wavelengths, choroidal lesions are highlighted because of infrared wavelength. Multicolor imaging was thus able to pick up choroidal lesions similar to NIR imaging.

Although OCTA for retinal vasculature has been described, OCTA for choroid has never been described for choroidal nodules in NF-1.[4] Incidentally, we were able to recognize retinal corkscrew vessels temporal to the fovea in superficial retinal plexus, which could be easily overlooked on biomicroscopy and other forms of imaging. The deep retinal capillary plexus was normal. These microvascular abnormalities are considered retinal markers of NF-1 though the exact nature of these remains unknown.[5]

Indocyanine green angiography (ICGA) has been used in the past to characterize choroidal lesions in NF-1.[36] These choroidal nodules are hypofluorescent on ICGA, which is believed to be because of persistent nonperfused lobules of choriocapillaris or blocked fluorescence due to choroidal nodules. OCTA at the level of choriocapillaris, in this case, showed low flow areas overlying the choroidal nodules. On OCT B scans, this was seen as thinning of choriocapillaris overlying choroidal nodules. The hyperflow (bright) areas of deep choroid on OCTA corresponding to the bright lesions on NIR imaging indicate rich vascular supply of these lesions. The hypofluorescence seen on ICGA in these lesions can thus be attributed low flow in the overlying choriocapillaris.

Conclusion

This report highlights multicolor scanning laser imaging as the potential alternative to NIR imaging for the detection of choroidal neurofibromatosis. OCTA is useful tool for the characterization of these lesions.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.