Posterior Segment Age-related Macular Degeneration
Figure 4: Outer Retinal Tubulations Observed with ‘En-face’ Spectral Domain Optical Coherence Tomography
A
The reason why such abnormalities develop is still not completely understood. Pseudocysts could correspond to Müller cell degeneration as seen in idiopathic macular telangiectasia type 2A and tamoxifen retinopathy. Anti-VEGF intravitreal injections have no effect on these cavities, which do not seem to be modified with time. Pseudocystic lesions, similar to those found in geographical atrophy, were described by Querques et al.19
in cases of exudative AMD in
association with fibrovascular scarring. These hyporeflective, intraretinal lesions present with typically squared edges. These pseudocysts are often multiple and their location can be very variable. They can be found in the external nuclear or ganglion cell layer but are most frequently situated in the internal nuclear layer. Their degenerative character is confirmed by the absence of angiographic signs and their stability. They are seen in 39 % of cases of exudative AMD complicated with a fibroglial scar. These pseudocystoid spaces probably correspond to retinal cell apoptosis.20
B
A: the branching tubular structure of outer retinal tubulations. B: The corresponding B-scan demonstrates two lesions (arrows) bordered by a hyper- reflective, well-defined rim located in the outer nuclear layer.
Another pitfall corresponds to CNV treated with anti-VEGF drugs and associated with epiretinal membrane. Sometimes, even if the CNV is closed, there is persistence of metamorphopsia associated with retinal thickening and pseudocysts. The diagnosis can be difficult and is based on the absence of improvement after anti-VEGF injection along with the absence of serous detachment and/or haemorrhages and exudates. This pitfall is more frequent in myopic eyes, where multiple pathologies are often associated.
•
Polypoidal vasculopathy. A false anti-VEGF resistance with persistent serous retinal detachment can occur in the case of polypoidal vasculopathy; this condition usually needs combination treatment for a better outcome.
It is particularly important to know that neovascular AMD that is refractory to a course of anti-VEGF monotherapy can harbour polypoidal choroidal vasculopathy.17
Polypoidal dilations might be
suspected on SD-OCT, but ICGA is the most valuable tool for revealing polypoidal lesions. In this pathology, it is recommended to combine the angio-occlusion of the polyps using photodynamic therapy and the anti-permeability effect of anti-VEGF therapy on the branching vascular network.
Pitfall 3 – Pseudocysts and Cystoid Cavities When a patient presents with intraretinal cysts during anti-VEGF treatment, the question is whether they are a sign of either exudation or degeneration? The cysts can be seen during routine AMD examination or during anti-VEGF treatment. Cohen et al.18 described hyporeflective cavities, located mainly in the internal nuclear layer but also in all other retinal layers, in dry AMD. He named these degenerative lesions ‘retinal pseudocysts’. These lesions have no walls and differ from retinal oedema in lacking retinal thickening. They are always located near an area of RPE atrophy (see Figure 3). They have no angiographic signs and can be found in 27 % of cases of geographical atrophy. They can also be seen during drusen resorption and are mostly found in the outer plexiform layer. The evolution of drusen has successive phases with first, an increase in drusen material and alteration of the surrounding tissues, followed by a disruption of the drusen, which is replaced by an atrophic area that can be correlated with pseudocysts.
Pitfall 4 – Outer Retinal Tubulations Outer retinal tubulations (see Figure 4) can be seen in both atrophic and exudative AMD. On B-scan SD-OCT, the outer tubulations are usually round, but they can also be elongated in shape, resembling a serous retinal detachment, in which case they have to be distinguished from CNV activity.
Zweifel et al.21
were the first to describe this aspect of retinal degeneration. Outer retinal tubulations represent a frequent finding as they are encountered in 56 % of patients with exudative AMD and in 20 % of cases of geographical atrophy.22
Outer retinal tubulations
have no angiographic translation and do not change with time. ‘En face’ SD-OCT analysis shows the arborised network of interconnected tubules. Their size ranges from 60 to 600 μm. They are located in the outer nuclear layer, below the outer plexiform layer and over, or contiguous to, a fibrous and hyper-reflective thickening of the CC–RPE complex or over an atrophic area of the CC–RPE complex. These structures are optically empty, bordered by a mild but well-defined rim, and tiny punctuations are visible inside or along the inner face of the rim. The existence of the rim and the punctuations inside allow one to differentiate easily the outer retinal tubulations from an oedematous cavity. The outer retinal tubulations have no specific clinical or angiographic signs; the differential diagnosis is mostly with other intraretinal cystoid cavities most frequently found in the outer plexiform layer.
Conclusion
In conclusion, even if anti-VEGF treatments are based on SD-OCT data, the discussed pitfalls must be taken into consideration. An overall analysis of the patient’s clinical examination, together with the imaging findings, is essential for accurate diagnosis and treatment of AMD. n
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