I have been understanding annulus to mean the 'ring' of the valve, to which the leaflets attach. This is circumferential and it can be a stenosis, but it would always be as a component of the valve. Can an annulus exist without a valve, as defined here?The types of malformations found by Dr. Zamboni in his published research have included:
- Annulus refers to significant circumferential stenosis of the whole venous wall;
- Septum/valve malformation refers to anomalous valve apparatus causing significant flow obstacles at the level of the junction of the IJVs with the brachiocephalic/anonymous trunk;
- Hypoplasia refers to under-developed long venous segments;
- Twisting refers to severe stenosies in consequence of a twisted venous segment;
- Membranous obstruction (web) refers to a membrane almost occluding a vein;
- Agenesis refers to the complete anatomical absence of a venous segment.
Valves are typically at the level of the junction of the IJVs with the innominate vein, but I thought septums could exist anywhere within the vein. A septum is not an anomalous valve aparatus but more of a sail or divider of the vein. I don't think they originate as valves but I don't know exactly how they do originate.
Hypoplasia can be long or short segments, but yes, underdeveloped veins. I do not think treatment of hypoplasias have been optimized. Low flow through hypoplasia increases the chance of clotting. Better to have a malformed valve or septum than a hypoplastic vein segment.
We don't hear much about membraneous obstruction and webs.
Agenesis may be the rarest of all of these.