Torpedo Maculopathy

Article initiated by:

Jaume Català-Mora, Manel Garcia-Mendieta

All authors and contributors:

Ignacio Flores-Moreno, Jaume Català-Mora, Jesus.Diaz, Koushik Tripathy, MD (AIIMS), FRCS (Glasgow), Manel Garcia-Mendieta, S. Grace Prakalapakorn, MD, MPH, Jason Hsu, MD, Jonathan C. Tsui, MD, Jennifer I Lim MD, Sarah Rodriguez

Assigned editor:

Jason Hsu, MD, Sarah Rodriguez

Review:

Assigned status Up to Date

 by Sarah Rodriguez on September 1, 2023.

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Torpedo maculopathy (TM), also known as solitary hypopigmented nevus of the retinal pigment epithelium (RPE), paramacular albinotic spot syndrome, congenital hypomelanotic freckle, or 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.

Torpedo maculopathy

ICD-10

[1]14.9

Disease Entity

Epidemiology

Shirley et al. published an eight-case series showing a slightly female predominance with a mean age at diagnosis of 8 years old (range 3-15). Based on this study, the prevalence was estimated to be 2/100,000 in subjects less than 16 years old who reside in Northern Ireland (Belfast), which is probably an underestimate given it is an asymptomatic condition .

Pathophysiology

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 the optic nerve, temporal to the 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 .
• A consequence of intrauterine chorioretinitis

Diagnosis

Manifestations

On exam, visual acuity is not generally affected since there is no foveal involvement and the lesion is usually an incidental finding. Nevertheless, central scotoma or microscotoma may be present at diagnosis. It is typically unilateral, flat, asymptomatic and non-progressive, although bilateral, crescent and satellite lesions have also been reported . Furthermore, an association with neurosensory retinal detachment or multifocal central serous chorioretinopathy has been published as well as one with a double-torpedo lesion . Only 4 cases have been reported in the literature of choroidal neovascularization (CNV) associated with TM, as it is typically stable . Owing to the RPE and outer retina damage, these lesions are susceptible to CNV development and need to be monitored. There is a characteristic hypopigmented torpedo-shaped area temporal to the macula, which points to the fovea with a hyperpigmented tail. The typical size is about two disc diameters horizontally by one disc diameter vertically, usually without foveal involvement .

Associations

Tsang et al. have theorized that TM may be associated with other systemic disorders such as kidney disease, blepharophimosis, situs inversus, choroidal nevi, and ametropias. Hansen et al. described TM in association with tuberous sclerosis and astrocytic hamartoma. However, Shields et al. maintained that there is no clear evidence of any systemic association.

Differential diagnosis

Condition	Entity
Old retinal lesions	Chorioretinal scar
Trauma	Retinal trauma
Congenital lesions	Congenital RPE hypertrophy Gardner syndrome-associated congenital RPE hypertrophy Congenital RPE albinotic spots
Tumors	RPE hamartoma Combined RPE-retinal hamartoma Benign melanoma or acquired
Retinal dystrophies	Viteliform dystrophy or pattern dystrophies

Clinical diagnosis

The pathognomonic lesion on funduscopic examination is solitary, hypopigmented, oval-shaped with hints of a bullet or a torpedo and a wedge-shaped tail extending peripherally and pointing toward the foveolar region along the horizontal raphe.

Figure 1. Hypopigmented flat bullet-shaped lesion temporal to fovea in the right eye.

Diagnostic procedures

Figure 2. Hyperfluorescent lesion containing some hypofluorescent spots (dead RPE).

• 

  Figure 3. Fundus autofluorescence of torpedo maculopathy showing mixed areas of hypoautofluorescence due to atrophic RPE cells and hyperautofluorescence likely due to stressed RPE cells
  Fundus Autofluorescence: Hyperfluorescent border (composed of lipofuscin produced by dysfunctional RPE cells or those under metabolic stress) surrounding the hypofluorescent area (atrophic or dead RPE), depending on the size involved .

Figure 4. A) OCT displays a Type 1 lesion with attenuation of interdigitation and ellipsoid zones without outer retinal cavitation. B) A Type 2 lesion: OCT shows cavitation in the outer retinal layers as well as loss of the ellipsoid zone.

• Optical Coherence Tomography (OCT): In 2015, Wong et al. proposed a classification of TM into two types according to the pattern of abnormality on OCT. In both types, there is 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 ellipsoid zone without outer retinal cavitation.
  • Type 2 show loss of ellipsoid and interdigitation zones as well as thinning of the outer nuclear layer associated with outer retinal cavitation. Inner choroidal excavation may be present or absent.
  • Type 3 lesions have been suggested as an additional category defined by excavated inner layers, retinal thinning, inner retinal hyper-reflective spaces, and no subretinal cleft .
  • Wong et al. postulated Type 1 lesions evolve into Type 2 ones over several decades, although this has been refuted by Shirley et al., asserting that the difference is phenotypical rather than temporal.

• 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 the 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 in the location of the lesion. Other findings range from diffuse attenuation of the choriocapillaris, hyporeflectivity due to atrophy correlating to the OCT subretinal gap and adjacent disruption near the tail . Choroidal vessels remain unaffected. OCTA en face imaging shows decreased flow in the area of the subretinal cleft associated with hyper-reflectivity in the tail area.

• Microperimetry: Reduction of retinal sensitivity along the torpedo lesion which remains stable during follow-up. Seldom, sensitivity may worsen over time owing to persistent alterations of outer retinal layers and choriocapillaris.

Management

In general, TM is a congenital condition that remains stable over years with minimal risk of vision loss. Nevertheless, due to the rare possibility of CNV or progression, periodic monitoring of these patients has been recommended. Patients can self-monitor as well with an Amsler grid, although in cases of large lesions or the presence of pigment clumping, more frequent observation may be indicated.