Intervenous tubercle of lower: True tubercle or normal interatrial fold?

Abstract

Richard Lower, in 1669, first described the tubercle that now bears his name, calling it the intervenous tubercle located between the fossa ovalis and the superior vena cava. The aim of the study was to confirm the existence of the tubercle as described initially by Lower, adding details of its location, dimensions, and prevalence. We examined 100 formalin-fixed human hearts. In no heart did we find any discrete tubercle or elevation of the right atrial wall superior to the superior limbus (rim) of the fossa ovalis. In addition, we could find no morphometric differences in the thickness of the area superior to the superior limbus of the fossa. Dissections revealed that very little of the extensive musculature can be removed without opening the right atrial wall and arriving outside the heart. This is the essential criterion in distinguishing folds from "true" septal structures. When viewed in this light, it is only the flap valve of the fossa ovalis, and its immediate muscular infero-anterior rim, the so-called lower limbus, that can be removed so as to create communications between the cavities of the atrial chambers, and not exiting at the same time from the cavities of the heart. This is because the larger part of the muscular borders of the fossa ovalis is no more than an infolding of the atrial walls, which incorporates extracardiac adipose tissue within the fold. Although this process of folding unequivocally produces an intracardiac buttress, namely, the limbuses (rims) of the fossa, the buttress, being an infolding, does not constitute, according to our definition, a true septum. On this basis, we suggest that it is the superior limbus of the fossa ovalis, or the superior interatrial fold, that previously has been considered to represent the intervenous tubercle of Lower.

Evolution and Development of the Atrial Septum

“…The right atrium of fully‐formed monotremes and marsupials always has a so‐called “torus of Lower” (Rowlatt, ). The torus, or tubercle, of Lower is considered to be the dorso‐cranial rim of the fossa ovalis (Loukas et al, ) (cf., Fig. E, structure 9).…”

Exploring the uncharted: Missing anatomical names in the Terminologia Anatomica

“…The intervenous tubercle ( tuberculum intervenosum ; eponym: tubercle of Lower) is a small projection located between the fossa ovalis and the opening of the superior vena cava in the posterior wall of the right atrium. It has been suggested that this buttress or infolding is, in fact, the superior limbus of the fossa ovalis or the superior interatrial fold (Loukas et al, 2012).…”

“…Therefore, the term foramina venarum minimarum (4036 in TA 2019) should be changed to ostia venarum minimarum, asKachlik and associates (2021) proposed.The intervenous tubercle (tuberculum intervenosum; eponym: tubercle of Lower) is a small projection located between the fossa ovalis and the opening of the superior vena cava in the posterior wall of the right atrium. It has been suggested that this buttress or infolding is, in fact, the superior limbus of the fossa ovalis or the superior interatrial fold(Loukas et al, 2012).The fibrous skeleton of the heart is a helpful term for the fibrous scaffold, comprised of dense connective tissue. Therefore, this termF I G U R E 1 A sagittal section through the lateral wall of the right nasal cavity.…”

Right atrial‐related structures in horses of interest during electrophysiological studies

“…13,38 A potential obstacle for transseptal puncture in horses via a cranial vena cava approach might be the intervenous tubercle, which can be identified as a triangular myocardial structure in the right atrium on transthoracic echocardiography. 43 In contrast to humans, the intervenous tubercle is prominent in horses, 15,44 and might hamper catheter navigation to the oval fossa. Moreover, the catheter needs to be curved sharply in order to aim towards the oval fossa.…”