Choroidal vasculitis as a biomarker of inflammation of the choroid. Indocyanine Green Angiography (ICGA) spearheading for diagnosis and follow-up, an imaging tutorial

Indocyanine green angiography (ICGA) is the gold standard to diagnose, evaluate and follow up choroidal inflammation. It allows clinicians to precisely determine the type and extension of choroidal vasculitis in the two main choroidal structures, the choriocapillaris and the choroidal stroma. The presence of choroidal vasculitis is often overlooked by the physician who often does not include ICGA in the investigation of posterior uveitis.

To describe choroidal vasculitis by analysing its ICGA signs in order to investigate and follow choroiditis and determine the pathophysiological mechanisms of inflammation of choroidal vessels.

The tutorial is presenting the normal findings in a non-inflamed choroid and the semiology of diverse choroidal vasculitis conditions, followed by practical illustrations using typical cases.

The two identified patterns of choroidal vasculitis corresponded on one side to choriocapillaritis appearing as areas of hypofluorescence depicting the involvement and extension of choriocapillaris inflammatory non-perfusion. The vasculitis of the choriocapillaris goes from limited and reversible when distal endcapillary vessels are involved such as in Multiple Evanescent White Dot Syndrome (MEWDS) to more severe involvement in Acute Posterior Multifocal Placoid Pigment Epitheliopathy (APMPPE), Multifocal Choroiditis (MFC) or Serpiginous Choroiditis (SC) with more pronounced non-perfusion causing scars if not treated diligently. On the other side, stromal choroidal vasculitis is characterised by leaking hyperfluorescent vessels that appear fuzzy and at the origin of late diffuse choroidal hyperfluorescence.

Choroidal vasculitis is present in almost all patients with inflammatory choroidal involvement, occlusive in case of choriocapillaritis and leaky in stromal choroiditis causing vessel hyperfluorescence, fuzziness of the choroidal vessels and late diffuse stromal hyperfluorescence on ICGA. Systemic vasculitis entities produce occlusive vasculitis of large choroidal vessels.