Torpedo maculopathy (TM)/ solitary hypopigmented nevus of the retinal pigment epithelium (RPE)/ paramacular albinotic spot syndrome/ congenital hypomelanotic freckle/ atypical macular coloboma was first described by Roseman and Gass in 1992, as a rare congenital anomaly of the RPE that produces a disruption of outer retinal layers . So far, short series and scarcely any data about prevalence, demographics or incidence have been reported. Pathogenesis remains unknown and the typical lesion is a single hypopigmented area in the macula, asymptomatic, temporal to fovea and with a characteristic torpedo-shape.
Shirley et al. published an eight-cases series showing a slightly female predominance, being the mean age at diagnosis was 8 years old (range 3-15). Moreover, starting from population studies, incidence was estimated as 2/100.000 in Northern Ireland (Belfast) citizens of less than 16 years old, probably underestimated since it is an asymptomatic condition, though .
Several theories have been proposed to explain the pathogenesis of TM:
- A developmental deficiency in the nerve fiber layer along the horizontal raphe  .
- Abnormal choroidal circulation or ciliary vasculature development .
- Persistent developmental defect in the RPE of the fetal temporal bulge, which is an aggregation of these cells occurring between 4 and 6 months of gestation. It is usually found at 4mm distance from optic nerve, temporal to fovea, progressively decreasing between 6 and 8.5 gestational months. There is therefore speculation about a congenital RPE defect at a given point in fetal development .
- As a consequence of intrauterine chorioretinitis .
On exam, visual acuity is not generally affected considering there is no foveal involvement, so that it is usually considered an incidental finding. Nevertheless, central scotoma or microscotoma can be present at diagnosis. It is mostly unilateral, flat, asymptomatic and non-progressive, although bilateral, crescent and satellite wounds are also reported   . Furthermore, association with neurosensory retinal detachment or multifocal central serous chorioretinopathy have been published  and a recent one with a double-torpedo lesion, as well . Only 4 cases have been issued in the literature of choroidal neovascularization (CNV) associated with TM, as it is commonly stationary  . Owing to the RPE and outer retina damage, these lesions are susceptible of CNV appearance and need to be close followed-up. There is a characteristic hypopigmented torpedo-shape area, temporal to macula, pointing to fovea with an hyperpigmented tail. The typical size is about two disc diameters horizontally by one disc diameter vertically, usually with foveal involvement .
Tsang et al. also hypothesize its association with other systemic disorders such kidney diseases, blepharophimosis, situs inversus, choroidal nevi, ametropias, whilst Hansen et al. described TM in association with tuberous sclerosis and astrocytic hamartoma. Notwithstanding, Shields et al. maintained there is no evidence of the systemic association.
|Old retinal lesions||
Funduscopic exploration is patognomonic: solitary hypopigmented oval-shaped, with hints of a bullet or a torpedo, with a wedge-shaped tail extending peripherally and pointing toward the foveolar region along the horizontal raphe.
- Fundus Autofluorescence: Hyperfluorescent border (composed by lipofuscin produced by dysfunctional RPE cells or those under metabolic stress) surrounding the hypofluorescent area (atrophic or dead RPE), depending on the size involved .
- Optical Coherence Tomography (OCT): In 2015, Wong et al.  proposed a classification of TM into two types according to the pattern of abnormality in OCT. In both types, there are attenuation of outer retinal structures (explained by RPE thinning and photoreceptor loss that can be attributed to several developmental defects  ) with an increased signal transmission along the choroid and conservation of inner layers.
- Type 1 include lesions that show attenuation of interdigitation zone and ellipsoids, without outer retinal cavitation.
- Type 2 show loss of ellipsoids and interdigitation zone as well as thinning of outer nuclear layer associated with cavitation. Choroidal excavation can be present or absent in Type 2 lesions, besides neurosensory retina; elevation does exist.
- However, it has been recently reported a Type 3 lesion, which is not included in the previous categories, defined by excavated inner layers, retinal thinning, inner retinal hypereflective spaces, and no subretinal cleft . Wong et al. postulated Type 1 lesions evolves in Type 2 ones over several decades, although this have been refused by Shirley et al. lately, asserting that the difference is phenotypical rather than temporary.
- OCT Angiography (OCTA): a recent non-invasive tool to study retinal and choroidal vasculature. The primary site of malformation lies in the RPE/choriocapillaris complex . There is a normal superficial retinal plexus and attenuation of signal in deep vascular layers along the lesion, with loss of deep vessels in the subretinal gap. Variations in deep retinal layers develop with time and are not on the location of the injury. Other findings range from diffuse attenuation of the choriocapillaris, hyporeflectivity due to atrophy correlating to the OCT subretinal gap and adjacent disruption near to the tail . Choroidal vessels remain unaffected. OCTA En face imaging shows decreased flow in the area of the subretinal cleft associated with hypereflectivity in the tail area.
- Microperimetry: Reduction of retinal sensitivity along the torpedo lesion which remains stable after follow-up. Seldom, it has been described sensitivity can worsen over time owing to persistent alterations of outer retinal layers and choriocapillaris.
In general, since TM is a congenital condition, it is thought that remains stable over years with no risk of vision loss. Nevertheless, considering the rare possibility of CNV or progression, it is strongly recommended periodically monitoring these patients, semiannual or annual . Patients can self-monitoring as well with an Amsler grid, although in cases of large lesions or the presence of pigment clumping, more frequent observation must be ensured.
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- Photo courtesy of Jaume.Catala-Mora MD.
- Photo courtesy of Ignacio.Flores-Moreno MD.
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