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Neovascular Phenotypes:RAP
(Retinal angiomatous proliferation)
11
Over 100 years ago, Oller described for the first time
the presence of anastomoses between the retinal and
choroidal circulations in eyes with disciform scars
(1)
.
Chorioretinal anastomoses were later described, asso-
ciated with laser photocoagulation
(2)
, radiotherapy
(3)
,
chorioretinal inflammatory diseases
(4)
and parafoveal
telangiectasias
(5)
. Anatomopathological studies of these
anastomoses were also undertaken in disciform scars
resulting from late age-related macular degeneration
(AMD)
(6)
. In 1992, Hartnett et al.
(7)
described nine cases
of retinal neovascularization, to which they referred as
“deep retinal vascular anomalous complex”. In 2000,
Slakter et al.
(8)
described chorioretinal anastomoses in
eyes with pigment epithelial detachment and indocya-
nine green (ICG) hot spots. In 2001, Yannuzzi et al.
described chorioretinal anastomosis as neovascular pro-
liferation with origin in the retina, and proposed the des-
ignation of RAP – retinal angiomatous proliferation
(9)
.
Several authors
(10-15)
maintained the designation of cho-
rioretinal anastomosis, proposing a choroidal origin for
this clinical entity. In 2008, Yannuzzi et al.
(16)
described
5 cases of RAP with the neovascular complex originat-
ing in the choroid instead of the retina, and proposed
that RAP should be called type 3 neovascularization.
However, RAP is still the most common designation.
2. Classification
According to Yannuzzi et al.
(9)
, the initial neovasculariza-
tion process in RAP consists of 3 stages:
i) Stage I – Intraretinal neovascularization. This stage is
mainly diagnosed when the second eye is already affected.
The presence of associated small retinal haemorrhages
constitutes a very useful sign in early RAP diagnosis. A
small elevation of the inner/intermediate retina caused by
angiomatous tissue may be observed under a slit lamp; this
elevation may extend tangentially, assuming telangiectasic
appearance. In FA, the angiomatous complex is observed as
a hyperfluorescent area in front of the RPE, identical to that
occurring in classic choroidal and, more frequently occult
neovascularization. Dilated retinal vessels may perfuse and
drain the intraretinal neovascularization (IRN) and form
retino-retinal anastomoses. ICG may reveal a hot spot with
staining and leakage.
ii) Stage II – Involvement of the subretinal space with local-
ized neurosensory detachment of the retina, oedema and
retinal haemorrhages at the edges may already be observed
in fundus colour photography. The angiomatous formation
draining vein becomes visible, originating in the deep retina.
PED is observed in 94% of eyes; FA may reveal well-delim-
ited hyperfluorescence in the diffuse leakage area associated
with PED, identical to that occurring for a minimally classic
choroidal neovascular membrane. ICG clearly establishes
stage II diagnosis as the presence of a hot spot with leak-
age, as well as a hyperfluorescent area associated with serous
pigment epithelium detachment (SPED). Leakage might
not be revealed by FA, probably because fibrin from retinal
exudates cannot be impregnated with fluorescein, contrary
to what occurs with ICG
(18)
. FA is rarely useful in differ-
ential diagnosis between classic, occult or minimally classic
membranes and stages I and II
(9)
, contrary to ICG, where a
slow-growing extra, juxta or subfoveal hot spot, sometimes
asymptomatic, is observed in stages I and II. Retino-retinal
anastomoses may also be observed in stage II.
iii) Stage III – Choroidal neovascularization is clearly visible,
sometimes with the appearance of vascularized PED.
According to Gass
(13)
, RAP would progress in 5 stages
instead of 3, easily identifiable by FA and ICG:
i) Pre-clinical stage – Atrophy of the outer retina, with retinal
capillaries moving closer to a choroidal neovascular complex
1. Introduction
Author:
Rufino Silva, MD, PhD
Coimbra University Hospital - Coimbra, Portugal
