Prepapillary vascular loop-a new classification

Abstract

Background/objectives: To analyze the ophthalmic characteristics of congenital prepapillary vascular loop (PVL) and to propose a new morphologic classification dividing the loops into six types.

Subjects/methods: Collaborative multinational multicentre retrospective study of PVL cases.

Results: There was a total of 49 cases (61 eyes), 37 unilateral (75.5%) and 12 bilateral (24.5%), 32 arterial type (65.3%) and 18 venous type (36.7%) (one patient had either kind in each eye). The mean number of loops per eye was 2.7 (range, 1-7). The loops were asymptomatic in 42 cases (85.7%). Other findings included: the presence of cilioretinal artery (14 cases), retinal vascular tortuosity (26 cases), amaurosis fugax (1 case), branch retinal artery occlusion (1 case) and vitreous haemorrhage (3 cases). Six morphologic loop types could be discerned based on elevation (flat vs. elevated), shape (figure of 8 or corkscrew with hyaline sheath), number (multiple or single), location (central or peripheral), lumen size (arterial vs. arteriolar) and presence of vascular tortuosity or vitreous traction.

Conclusions: PVL are usually asymptomatic and can be divided into six morphologic types with different pathogenesis during early embryogenesis.

Fig. 1. Schema of spectrum from tortuosity to grades of loop formation (Top).

Loop morphology divided into six types (Bottom): Type 1—Flat central single intraretinal loop or twist without associated findings; Type 2—Flat central intraretinal loop with generalized retinal vascular tortuosity; Type 3—Flat radial small loops (arteriolar or venular); Type 4—Loop protrude into vitreous as figure of 8; Type 5—Vitreous corkscrew loop; Type 6—Any loop with associated vitreous traction.

Fig. 2. Type 1 and 2 loops.

Top composite. Right eye semi-loop (arrowhead) (a) and left eye flat arterial loop type 1 (arrow) (b). Middle composite. Bilateral (c, d) venous type 2 loops and normal anatomy of retina and disc by optical coherence tomography angiography. Bottom composite. Retinal venous tortuosity with type 2 venous loop in right eye (e).

Fig. 3. Type 3 loops.

Left composite. Bilateral multiple sector of small corkscrew Type 3 venous loop (arrows) (a) (with permission from Image Bank^© 2019 American Society of Retina Specialist) Right composite. Venous loop type 6 (arrows) in the right eye (b) with 20/20 vision and normal intravenous fluorescein angiography transit (c). Optical coherence tomography through the loop of the right eye demonstrates vitreous traction (white arrow) (d). The left eye shows vitreo-papillary traction (white arrow) without presence of a loop (e).

Fig. 4. Type 4 loops.

Top composite. Type 4 arterial loop right eye (a) and Type 4 venous loop left eye (b). OCT (c) and OCTA (vitreous scan) (d) demonstrate the left venous loop protruding into Cloquet canal. Bottom composite. Type 4 arterial loops as figure of eight configuration with 4 loops (left bottom) (e) and 7 loops. (right bottom) (f: right eye; g: left eye).

Fig. 5. Type 5 loops.

Left top composite. Left eye with Type 5 prepapillary arterial loop (arrow) (a, b) with cilioretinal artery and retinal vascular tortuosity. Left middle composite. Type 5 loop corkscrew arterial loop (white arrow) (c) with the direction of flow shown on fluorescein angiography by black arrows (d) (with permission from Image Gallery^© 2019 American Academy of Ophthalmology and Image Bank^© 2019 American Society of Retina Specialist). The loop is surrounded by a fibroglial sheath that is probably a remnant of Bergmeister’s papilla. Optic disc pallor and sheathing of cilioretinal artery are results of prior toxaemia of pregnancy 15 years earlier. Left bottom composite. Straight variant of type 5 loop (3 arrows) (e) follows the Cloquet canal into the vitreous and is surrounded by a glial sheath (with permission from Image Gallery^© 2019 American Academy of Ophthalmology). Right top composite. Type 5 bilateral arterial loops. OCT shows different level of looping and fibroglial sheath. Severe tortuosity of the retinal vasculature with inferior peripapillary twisting of the artery over the vein in the right eye (arrowhead) (f) and arterial looping just above the disc in the left eye (arrowhead) (g). Right bottom composite. The right eye has Type 5 arterial loop (arrow) (h). The left optic disc has a semi-loop (arrowhead) (i).