FIG 51.14 Aortoventricular tunnel opening into the roof of the right ventricle (A) Anterior view, with the tunnel (as shown in Fig 51.13) taking its origin from the right coronary aortic valve sinus (B) However, the tunnel (shown by the red cord), opens into the infundibulum of the right ventricle adjacent to the medial papillary muscle FIG 51.15 Essential feature of an aortoventricular tunnel (arrow) that opens to the left ventricle The tunnel bypasses the hinge of the leaflet of the aortic valve, which is detached from its usual origin from the aortic valvar sinus Explanations for the morphogenesis of the lesions have been legion However, as we have shown, not only the arterial valvar sinuses but also the valvar leaflets, are formed within the intermediate part of the outflow tract Furthermore, the outflow cushions also muscularize to produce the subpulmonary infundibulum When these developmental events are coupled with analysis of the structure of the lesions, they favor the notion that the lesions represent abnormal molding of the central cushion mass In this regard, it cannot be coincidental that almost all tunnels reported thus far, with the exception of those joining to the right atrium, have involved the aortic sinuses adjacent to the pulmonary trunk Many previous accounts have suggested that the tunnels involve the infundibular, or muscular outlet, septum Because such a septum does not exist in the normal heart, explanations involving such a “septum” cannot be correct As we have shown, as the central cushion mass matures, it becomes converted not only into the freestanding muscular subpulmonary infundibulum, but also the fibroadipose tissues that interpose between the infundibulum and the aortic root The tunnels are found within this area usually occupied by fibroadipose tissue (see Figs 51.13 and 51.14), irrespective of whether they open to the right or the left ventricle It is less than satisfactory that the lesions continue to be described as “tunnels,” particularly those terminating in the right atrium, but this is unlikely to change Understanding comes from the appreciations that the lesions opening in the ventricles represent abnormal formation of the arterial valvar sinuses and leaflets Those that empty to the left ventricle typically represent little more than separation of the hinge of the valvar leaflet from the supporting sinus The involvement of the adjacent aortic valvar sinuses in their formation also explains why so many of the tunnels also involve the coronary arteries as part of the malformation The atrial tunnels are more akin to the fistulous communications discussed earlier Aorto–left ventricular tunnels are extremely rare congenital heart defects Although first reported by Levy et al in 1963,46 descriptions since then have been limited to isolated case reports and small case series In a single-center cohort from Boston Children's Hospital, details of only 11 patients were reported over a 35-year period.47 Due to the rarity of the lesion, it is commonly misdiagnosed.48 It is important to distinguish aorto–left ventricular tunnels from isolated native aortic valve regurgitation, coronary artery fistulas, and ruptured sinus of Valsalva aneurysms The aortic part of the tunnel is made from the aortic wall The tunnel originates above the sinutubular ridge, a feature that distinguishes it from a ruptured sinus of Valsalva aneurysm, which originates from the aortic sinuses themselves The entrance into the ventricle is at the triangular region between the right and left coronary artery sinuses.49 The coronary arteries are frequently involved in the defect as well,6,47,49,50 and the origin or the right coronary artery is usually situated below the sinutubular ridge and there may be prolapse of the right coronary leaflet.49 In some cases, the right coronary artery originates form the tunnel itself.50 Although usually the origin of aorto–left ventricular tunnels are above the right coronary sinus, rarely they can originate from above the left and noncoronary artery sinuses.50–53 Associated lesions may be present, particularly of the aortic valve and coronary arteries.47