14a above — a very rarely seen by Digital Subtraction Angiography, but much more commonly with Cone Beam / Flat Panel CT, tiny vessel or vessels arising from the “hypophyseal” segment of the internal carotid artery — a proximal intradural segment also known as supraclinoid, paraophthalmic, etc. See ICA page for details of this semantic disorder.
The artery arises from the medial carotid wall — pituitary is medial to the carotid — and supplies the hypophysis, by definition — the pituitary — usually anterior hypophysis and pituitary stalk. The inferior hypophyseal arteries (from the MHT) are usually much bigger and supply the posterior pituitary.
The “hypophyseal aneurysm” — a medially or inferiorly projecting aneurysm from the hypophyseal segment — is thought to be related to this branch — at least by those who believe that aneurysms must arise from branch points. Aneurysms, of course, don’t care for our opinions, but we are right more often than not.
If you want to see hypophyseal arteries, do some high res DYNA of VASO imaging.
Case courtesy Dr. Eytan Raz — here is a beautiful example of a very dominant superior hypophyseal artery (arrow) supplying the posterior hypophysis (arrowhead), with a correspondingly small inferior hypophyseal contribution from the MHT (dashed arrow)
Cross eye stereo
View from the back — again small inferior hypophyseal, big superior hypophyseal — balance again… See the beautiful vascular ring of the posterior pituitary — the connecting it with the contralateral side
MIP image shows the sella nicely — and helps prove its posterior pituitary
Pure arrowless images — easier to steal…
Of course, there is an aneurysm here — the branch point camp would point out how this larger than usual branch is a setup for aneurysmal formation. Naturally…
Supply of the Hypophysis and Balance
As always neuroangio is about balance. There may be one or more superior hypophyseal arteries. Usually one is visible by cone beam/flat panel CT. Sometimes more than two. Here there are 3. Nicely shown is supply of the stalk (open arrow). There is also likely contribution to the optic chiasm, which is of course very important. The inferior hypophyseal branches (dashed arrow) from the MHT support the posterior pituitary. The ILT is hypoplastic, with lateral branches of the MHT (white arrowhead) heading towards the meckel cave and the recurrent branch along the tentorial edge (black arrowhead) supplying territory normally done by the ILT
The image below is from an Ophthalmic Artery case page. The superior hypophyseal branches supplying the stalk are dashed white arrows. Inside the oval are vessels related to the optic nerve and chiasm — possibly in part supplied by the superior hypophyseal branches also, but not sure.
Axial source data movie — pause and scroll
Optic Nerve Supply
Unlike in the case above, here superior hypophyseal (arrow) supply of the intracranial optic nerve (oval) and possibly chiasm is shown definitively (lower right image is coronal)
Best seen in this movie (pause to scroll)
Pattern of optic apparatus supply and unusual hypophyseal ILT vessel
VR — the anterior-most branch of the superior hypophyseals is usually the largest (arrow). The others are too small to see on a VR image
MIPS. The anterior, proximal-most branch (arrow) tends to supply the optic nerve (white oval), while the more posterior branches (dashed arrows), when present, supply more posterior structures such as chiasm and tract (dashed oval)
A highly unusual branch originating from ILT region swings underneath the cavernous ICA and supplies the floor of the pituitary fossa. Yet unknown, as far as i know
“Carotid Fenestration” — hypophyseal to PCOM connection
Super case by Dr. Eytan Raz
see that small branch to the anterior hypophysis?
Relationship with Ophthalmic Artery
Another interesting topic. Courtesy Eytan Raz MD PhD. Hypophyseal Aneurysm, post PED
Follow up — notice a “lower” origin of the ophthalmic now, and a small vessel (arrow) from the medial wall, adjacent to the new ophthalmic ostium.
What happened to the ophthalmic origin? See Pipeline Device Properties page for more into. Basically, the Pipeline is not fully apposed to the ophthalmic ostium, creating a secondary communication between the aneurysm and the ophthalmic — essentially incorporating the ophthalmic ostium into the aneurysm. As the aneurysm shrinks, the flow to ophthalmic is reorganized. Other examples are on the Pipeline page.
Fine. But what about the little branch — the superior hypophyseal artery?
Whats interesting is that the superior hypophyseal was part of the aneurysm. Now that the aneurysm has shunk its ostium has come to appose the Pipeline, and its flow is preserved. Other interesting things are there too.
Power of Cone Beam CT imaging
Even the smallest superior hypophyseal arteries can be seen with advanced cone beam CT. Top left is an already high resolution cone beam CT volume rendered image with no apparent Superior Hypophyseal. Windowing to increase sensitivity allows for visualization of a tiny superior hypophyseal (arrow) — top right image. Bottom row are axial (left) and coronal (right) MIP images, showing the same artery, as well as beautifully seen pituitary stalk (dashed arrow)
Superior hypophyseal supply of the Optic Nerve
Important point here — since with increasing visualization of this vessel comes possibility of intervention there. Here is an example of superior hypophyseal artery (arrows) supplying the intracranial and optic canal portions of the nerve (dashed arrows). Any ischemia here (posterior ischemic optic neuropathy) would be quite obvious to the patient. Careful now…
Balance — MHT (with inferior hypophyseals) is large (arrow), also supplying anterolateral territory (dashed arrow) of correspondingly hypoplastic ILT. A superior hypophyseal artery is shown by arrowhead
PCOM- superior hypophyseal balance
The balance between these two is rarely discussed. Here, superior hypophyseal is markedly hypoplastic (dashed arrow). Supply to pituitary and optic chiasm is via a prominent branch (arrows) from the proximal PCOM
Posterior Pituitary Supply — MHT Balance
Spectrum and balance again. Usually, the inferior hypophyseal branches from the MHT supply the posterior pituitary. Here, the MHT is well-developed, but primarily supplies the free margin of the tentorium, while the posterior pituitary is fed by the superior hypophyseal branch (arrow).
Same case MHT — the larger trunk (dashed arrow) is mainly marginal tentorial, smaller one (arrowheads) is clival branches inferiorly towards anastomoses with ascending pharyngeal counterparts
Patent Superior Hypophyseal artery (arrow) post Pipeline Embolization Device placement (6 months post).
Note stenosis at the proximal segment of the device due to the proximal edge terminating on the curve of the anterior genu (dashed arrow). This is a kind of T-bone configuration which usually heals with a stenosis.
Another example, in setting of multiple aneurysms. Post clipping of ruptured ACOM and bystander MCA aneurysm, and subsequent Pipeline Shield Embolization of a small ACOM residual. Stereo images show presence of Ventral Ophthalmic Artery origin from proximal A1. The Pipeline is placed distal to its origin, just in case.
MIPS — great anatomy of the MHT, ILT as well. The MHT is somewhat hypoplastic. ILT supplies bulk of its territory via the recurrent tentorial artery. There are 3 superior hypophyseal arteries, supplying large portions of the optic nerve, chiasm, and probably some proximal tract, together with the PCOM