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Septa of the Heart
The atrial septum consists of 3 parts; The most superior is the septum derived from the sinus venosus (purple), the middle is the septum primum (green) and the most inferior is derived from the endocardial cushions (pink) The endocardial cushions also contribute to the formation of the of the membranous component of the interventricular septum. The interventricular septum consists of the membranous septum and the muscular septum (red). The great vessels are separated by a muscular conal septum (orange) and the membranous aorticopulmonary septum (light pink).
Ashley Davidoff MD TheCommonVein.net

The Conal septum had two little lambs (Ao and PA)

And everywhere the conal septum went

The sheep were sure to go

MusclesBands Between the Inflow and Outflow Tract of the Right Ventricle (RV
Thr superior aspect of the septal band (green) has two limbs – the “Y” of the septal band. and the conal septum (blue) embeds itself in the Y of the septal band. The (chordae) of the conal papillary muscle (aka papillary muscle of Lancisi- white arrow) also inserts in the “Y ” of the septal band. The anterolateral papillary muscle (yellow) )originates from the septal band) and subtends the anterior leaflet of the tricuspid valve . The moderator band (purple) connects the septum to the the free wall, and the parietal band (orange) completes the muscular ring that separates the inflow from the outflow tract. The pulmonary valve (above the parietal band and conal septum) defines the border between the RVOT and conus with the pulmonary artery.
Ashley Davidoff MD
06409 RV muscle bands b01.81
Magnification of the conal septum lying in th ‘Y” of the septal band
Ashley Davidoff MD TheCommonvein.net
Conal Septum (CS) as viewed from the RVOT
The conal septum lies in the ‘Y” of the septal band (sb) and the medial tip of the parietal band (pb). The pulmonary artery lies superior and to the left of the the conal septum and the aorta lies posterior and the conal septum. Since the conal septum lies between to the two great vessels, any change in its position affects both great vessels. If for example it moves posteriorly toward the aorta, it will cause subaortic stenosis, and if it moves leftward it will cause subpulmonary stenosis.
Ashley Davidoff MD TheCommonvein.net

normal Conal Septum in Tetralogy of Fallot (TOF) (Monology of Stensen)
In TOF the conal septum (purple) is too small resulting in a VSD, (black hole) and also misaligned toward the left and anterior causing subpulmonary infundibular stenosis and an overriding aorta. Since the aorta and PA are bound together by the conal septum – shift of the conal septum results in movement of both. The subpulmonary stenosis results in decreased forward flow and hence structures distal to the infundibulum may become hypoplastic, dysplastic or aplastic. Associated anomalies for example include absent pulmonary valve (PV) pulmonary stenosis or atresia, stenotic branch pulmonary stenosis, or absent pulmonary arteries
Ashley Davidoff MD
TheCommonVein.net

Tetralogy of Fallot
THe deficient and malaligned conal septum
Ashley Davidoff MD TheCommonVein.net

 

Abnormal Conal Septum in Tetralogy of Fallot (TOF) (Monology of Stensen)
In TOF the conal septum (purple) is too small resulting in a VSD, (black hole) and also misaligned toward the left and anterior causing subpulmonary infundibular stenosis and an overriding aorta. Since the aorta and PA are bound together by the conal septum – shift of the conal septum results in movement of both. The subpulmonary stenosis results in decreased forward flow and hence structures distal to the infundibulum may become hypoplastic, dysplastic or aplastic. Associated anomalies for example include absent pulmonary valve (PV) pulmonary stenosis or atresia, stenotic branch pulmonary stenosis, or absent pulmonary arteries
Ashley Davidoff MD
TheCommonVein.net
Cardiovascular imaging approach in pre and postoperative tetralogy of Fallot
Sotiria C. Apostolopoulou, Athanassios Manginas, Nikolaos L. Kelekis & Michel Noutsias
BMC Cardiovascular Disorders volume 19, Article number: 7 (2019)
CT of Tetralogy of Fallot
The Common Vein.net

 

 

Angiography of Tetralogy of Fallot (TOF) with Hypoplastic Pulmonary Arteries
The RV angiogram (a, b) shows a stenotic infundibulum in the A-P projection (white arrow) and lateral projection The overriding aorta fills later through a VSD. The second series is an LV gram (c,d) with catheter entering the RA, passing through an ASD into the left atrium and then LV. The aorta is well opacified and is normal in size in contrast to the smaller main pulmonary artery, and branch pulmonary arteries
Ashley Davidoff MD TheCommonVein.net
Angiography of Tetralogy of Fallot (TOF)
The angiogram shows a catheter entering the right atrium and RV from the IVC. Contrast injected into the RV traverses a stenotic infundibulum in the A-P projection (blue arrow) ? (a -magnified in b ) and lateral projection (e and magnified in f) The overriding aorta fills later through a VSD – (red arrow ? c and magnified in d)
Ashley Davidoff MD TheCommonVein.net
Angiography of Tetralogy of Fallot (TOF) with Hypoplastic Pulmonary Arteries
The RV angiogram in the A-P projection shows a stenotic infundibulum , dysplastic appearing pulmonary valve region, supravalvar stenosis, hypoplastic main pulmonary artery and a dilated right pulmonary artery The overriding aorta fills later through a VSD.
Ashley Davidoff MD TheCommonVein.net
Pathologic anatomy of TOF. (a, b) Axial black-blood MR images show infundibular pulmonary stenosis (arrow in a) and right ventricular hypertrophy (arrowheads in b).
(Frank L et al Cardiovascular MR Imaging of Conotruncal Anomalies Radiographics)
Pathologic anatomy of TOF. (a, b) Axial black-blood MR images show infundibular pulmonary stenosis (arrow in a) and right ventricular hypertrophy (arrowheads in b). 
(Frank L et al Cardiovascular MR Imaging of Conotruncal Anomalies Radiographics)
Pathologic anatomy of TOF. (c) Oblique sagittal SSFP MR image shows the aorta (A) overriding the right ventricle (RV) with a subaortic ventricular septal defect (arrow).The ascending aorta is dilated. LV = left ventricle.
(Frank L et al Cardiovascular MR Imaging of Conotruncal Anomalies Radiographics)
Pulmonary artery atresia and stenosis in TOF. (a) Volume-rendered image from gadolinium-enhanced 3D MR angiography in a neonate with TOF shows absence of the left pulmonary artery (LPA). Note the right-sided aortic arch and normal right pulmonary artery. (b) Volume-rendered image from gadolinium-enhanced 3D MR angiography in an adult patient with TOF depicts bilateral pulmonary artery stenoses. LPA = left pulmonary artery, MPA = main pulmonary artery, RPA = right pulmonary artery, RV = right ventricle.
(Frank L et al Cardiovascular MR Imaging of Conotruncal Anomalies Radiographics)
Pulmonary artery atresia and stenosis in TOF. (a) Volume-rendered image from gadolinium-enhanced 3D MR angiography in a neonate with TOF shows absence of the left pulmonary artery (LPA). Note the right-sided aortic arch and normal right pulmonary artery. (b) Volume-rendered image from gadolinium-enhanced 3D MR angiography in an adult patient with TOF depicts bilateral pulmonary artery stenoses. LPA = left pulmonary artery, MPA = main pulmonary artery, RPA = right pulmonary artery, RV = right ventricle.
(Frank L et al Cardiovascular MR Imaging of Conotruncal Anomalies Radiographics)
Absent pulmonary valve in a neonate with TOF. Axial black-blood MR image shows markedly enlarged central pulmonary arteries. The left main bronchus (arrow) is compressed by the enlarged left pulmonary artery.
(Frank L et al Cardiovascular MR Imaging of Conotruncal Anomalies Radiographics)

 

Anomalous coronary artery origin in a neonate with TOF. Oblique axial image from a whole-heart 3D SSFP acquisition shows anomalous origin of the left anterior descending (LAD) coronary artery from the right coronary artery (RCA). Note that the left anterior descending coronary artery crosses the RVOT. A = aorta, br = branch, LCX = left circumflex coronary artery.
(Frank L et al Cardiovascular MR Imaging of Conotruncal Anomalies Radiographics)

 

Aortopulmonary collateral vessels in an infant with TOF and main pulmonary artery atresia. Preoperative volume-rendered image from gadolinium-enhanced 3D MR angiography reveals a large collateral vessel (gray) that arises from the right subclavian artery (gray) and supplies the right lung and another large collateral vessel (brown) that arises from the descending thoracic aorta and supplies the left lung. The central pulmonary arteries (green) are small and confluent.
(Frank L et al Cardiovascular MR Imaging of Conotruncal Anomalies Radiographics)

 

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