|Originating from the proximal cavernous segment of the ICA, the MHT may come off as a single trunk or a collection of vessels. MHT vessels supply the posterior pituitary and portions of the clivus, CN III, IV, V, and VI, pituitary gland, tentorium cerebelli, and adjacent dura. Extensive collateral pathways exist with the ILT, MMA, and hypoglossal branch of the ascending pharyngeal artery.
MHT. The “classical” main branches of the MHT (A)B: Lateral Tentorial Artery along the lateral edge of the tentorium, and in hemodynamic balance with petrosquamosal branches (L) of the MMA and Occipital Artery (O); C: Marginal Tentorial Artery a.k.a. Bernasconi-Cassinari along the free edge; D: Inferior Hypophyseal Artery, branching into:
E: Hypophyseal branches supplying the posterior and parts of anterior pituitary and anastomosing with each other (see Carotid Agenesis)
F: Inferior Clival Branch descending along the dorsum sella where it is in hemodynamic balance with the ascending clival braches (K) of the Ascending Pharyngeal
G: Lateral Clival artery, branching into:
H: Lateral Branch of the Lateral Clival artery which runs alongside the Superior Petrosal Sinus
I: Medial Branch of the Lateral Clival Artery which runs alongside the Inferior Petrosal Sinus and is in balance with Jugular branches (J) of the Ascending Pharyngeal
Most MHT will not look anything like this. Variation is the rule and most of these branches are too small to see in normal state anyway. Important anastomoses also include branches of the ILT (N) such as recurrent marginal artery, the foramen lacerum branch of the Middle Meningeal Artery (M), and Occipital Artery (O). The skull used in this photo was provided courtesy of Dr. John Loh, NYU Langone Medical Center
A discernible MHT on MRI/MRA or CT angiogram usually means some kind of pathology. The normal MHT is much to small to be resolved on a 1.5T system, although on 3T a prominent but still normal MHT may be seen on occasion. If you happen to see one, look carefully for other problems. You will not miss a huge meningioma within which said MHT will be embedded. What’s much harder to see on MRI/MRA is a dural fistula, so make sure to look for one carefully. If you are a radiologist reading the study and dural fistula is a potential concern of the referring doc, seeing the MHT should be strong enough indirect evidence to proceed to a catheter angiogram. CT angiography may be more sensitive as spacial resolution is better than MR techniques but the same advice applies — it is usually abnormal.
Contrast T1 MRI (left) and TOF MRA (right) of a patient with large petroclival meningioma invading the cavernous sinus with a pathologically hypertrophied MHT branch sullying the tumor.
TOF-MRA demonstrating hypertrophied MHT and ILT branches supplying a large petrous apex fistula. Smaller fistulas, particularly dural ones, may be very hard to see apart and, apart form visualizing an unusually large feeding vessel, the study looks normal. The best policy in such cases is to tailor the index of suspicion to match study indication.
Lateral angiogram early arterial phase demonstrating typical appearance of the MHT — nothing is visible. The size of normal MHT is highly variable — depending on AP, ILT, MMA, and other dural vessels with which it is in balance — a prominent MHT means relatively small contribution to its dural territory from the others.
Later arterial phase imaging of the same case demonstrates a pituitary blush — inferior hypophyseal artery would be the source. No distinct MHT component vessels are visualized. Variability is the rule, and parts of the MHT may be visible in various non-pathologic circumstances.
MHT Fakeout: Inferior temporal MCA branches often project in the region of the MHT on the lateral projection (red). On careful evaluation one can see that these vessels actually originate more rostrally (green arrow) from the MCA.
Inferior Hypophyseal Artery
Inferior Hypophyseal Artery of the MHT opacifying the pituitary gland with a characteristic blush (no adenoma here!). The branch to the pituitary is well seen on the AP projection usually best visualized in mid-arterial phase and persisting into venous phase. The posteroinferior branch of the MHT classically supplies the neurohypophyisis and portions of the adenohypophysis, although in this case the supply appears to be more extensive. Also notice absence of the ophthalmic artery (see meninigo-ophthalmic variant on the MMA page).
Pituitary Gland visualization on rotational angiogram. The rotational is acquired via a long (approximately 6 second) injection while the x-ray camera sweeps an arc around its target. The data is then reconstructed into a 3-D image. Because of long injecting timing, the pituitary plexus is visualized likely in venous phase. The images below (patient with a pseudoaneurysm of the sphenoid sinus ICA portion in setting of chronic sinusitis) demonstrate little pituitary blush on conventional angio and the inferior hypophyseal branches are not particularly prominent. However the rotational angio, because of long injection timing, shows a vascular plexus within the gland.
Aneurysm=dark blue. MHT inferior hypophyseal branch=light blue on 3-D and purple on lateral angio; ICA medial wall dehiscence=orange; pituitary plexus on 3-D and pituitary blush =red
Another demonstration of the inferior hypophyseal artery, along with the marginal tentorial (see below)
Red= inferior hypophyseal, white=pituitary blush; purple = marginal tentorial, blue = ILT; purple = ? rotundum branch; orange = ? ovale branch
Primitive Maxillary Artery: The inferior hypophyseal arteries in the embryo are called primitive maxillary arteries. The left and right inferior hypophyseal counterparts anastomose with each other normally and supply the pituitary gland as above. In cases of carotid agenesis involving the petrous segment, the carotid artery can be reconstituted via the contralateral carotid thru thisprimitive maxillary anastomosis. This results in a bizzare large vessel traversing the pituitary fossa connecting one carotid artery to the other, as can be seen below.
Hypophyseal Branches: MHT to MHT anastomosis with carotid reconstitution
As in above case of primitive maxillary artery, left to right MHT anastomoses may re-emege in setting of carotid occlusion. In this patient with insufficient ACOM, the right carotid is occluded. Reconstitution is afforded via accessory meningeal supply to the ILT (see ILT) and via left to right hypophyeseal branches of the MHT, shown below.
Light blue=left MHT; purple=hypophyeal branches of the left and right MHT along the clivus; yellow=right MHT; red=carotid; blue=MCA
Dural fistula, the anatomists best friend: Perhaps the best way to study various dural branches is by looking at fistula cases, where all kinds of very small arteries can be demonstratively enlarged.
Branches of the MHT:
Marginal Tentorial Artery — a.k.a. Bernasconi-Cassinari — one of the few remaining named branches, it was described by those men in their study of tentorial notch meningiomas. This artery runs along the medial edge of each tentorial leaf (a.k.a. Tentorial Incisura) towards to torcula. It is difficult to tell this artery apart from the lateral tentorial arcade — which is the artery that runs from the MHT along the lateral aspect of the tentorial leaf towards the sigmoid sinus. On the AP the distinction is easy. The marginal tentorial artery participates in supply of adjacent cranial nerves and dura.
Lateral projection of a vein of Galen dural fistula in an elderly man (blue arrow points to enlarged vein of Galen). Multiple small vessels run along the medial edge of the tentorium from the MHT (red arrows) to particupate in the fistula. Typically one sees a single maginal tentorial branch but in case of high flow fistulas like this one innumerable tiny feeders develop to the point where the dura is carpeted with vessels (see cases in Ascending Pharyngeal Section as well). PCA and ACA feeders are also prominent. Also notice transosseous branches of the middle meningeal (black) and superficial temporal artery (orange) going towards high convexity and dumping into arterioles of the falx cerebri (green) leading towards the fistula.
Marginal Tentorial collateral pattern.
Lateral (top) and AP (bottom) images of a patient s/p left pterional craniotomy for attempted clipping of an ophthalmic artery aneurysm. The surgery was aborted. The MMA has been sacrificed during the craniotomy. The marginal tentorial artery is secondarily enlarged and now assumes supply of the falx cerebri (purple arrows). Notice the upward course of the marginal tentorial, following the incisura. The lateral tentorial has a more straight or downward-pointing course on the lateral following the course of the petrous apex, which can be well seen on the native images. Also notice, incidentally, an unusually large anterior branch of the MHT (red) which is participating in supply of the orbit in this patient. The ophthalmic artery is marked in blue.
Prominence of MHT and ILT post craniotomy
Top images demonsrate and AVM pre and post embolization. Bottom row stereo pair shows better visualization of the MHT and ILT branches following ipsilateral craniotomy with MMA sacrifice. Blue=MHT descending clival branches; Light blue=marginal tentorial arcade; Purple = ILT
The same case, 3-D stereo view.
Stereo View of the marginal tentorial artery, which first courses somewhat laterally (see MRA above) and subsequently turns medial towards the falconentorial junction and ascends along the posterior free edge of the falx. The patient is status-post pterional craniotomy and secondary MMA sacrifice.
Marginal Tentorial in case of radiation vasculopathy
An unfortunate child extensively irradiated in his home country with subsequent development of radiation angiopathy. A moya-moya pattent is seen on this ICA injection. An absolutely enourmous recurrent meningeal artery (red) arising from a large ophthalmic (blue) supplies portions of the cerebral hemipheres thru pial collaterals. Notice ACA evidence of ventriculomegaly and a large anterior ethmoidal artery (yellow) giving rise the the artery of the falx cerebri (pink). The choroidal blush is labeled in green. A large marginal tentorial artery (Bernasconi-Cassinari) is supplying the posterior falx cerebri (black)
Lateral Tentorial Artery: As above, this artery is a branch of the MHT that runs along the lateral edge of the tentorium cerebelli and along the sigmoid sinus. Given that sigmoid sinus is a relatively common location of dural fistulas, this artery is in perfect position to supply it nearly every time. This vessel is easy to differentiate from the Marginal Tentorial by its straight course off midline towards the sigmoid sinus on frontal projections.
Lateral projection demonstrating the lateral tentorial arcade branch (red) extending towards a small arterial channel within the wall of the sigmoid sinus (orange) to supply a simoid sinus fistula (blue = early sigmoid sinus vein). Notice inferior direction of the vessl, in contrast to the marginal tentorial artery (see above)
The same case — lateral tentorial arcade in AP projection.
Dural Fistula — MHT supply
Lateral Left ICA injection demonstrating a dural cavernous carotid fistula with prominent MHT supply (brown arrow). Also notice supply from the recurrent meningeal branch of the ophthalmic artery (red). Drainage is primarily into the ophthalmic vein (blue)
Same case, demonstrating hypoglossal division of the ascending pharyngeal artery (red, and letter H on the top illustration) contribution to the fistula on the left, and MMA (green, letter G on top illustration) and foramen rotundum branch (yellow) contributors on the right image. See also Ascending Pharyngeal section.
Dural Fistula — MHT supply II
A dural fistula initially thought to be a glomus jugulare tumor on MRA. The fistula is supplied by enlarged lateral tentorial artery of the MHT and via branches of the occipital and ascending pharyngeal (musculospinal and sigmoid sinus branches) arteries. Notice the characteristic lateral course of the lateral tentorial artery along the petrous ridge.
MHT Lateral Tentorial = red; Occipital=yellow; ascending pharyngeal (jugular division of the neuromeningeal trunk) = pink; arterialized flow in the sigmoid sinus=purple. The bottom right image is generated by using arterial phase mask in the brain venous phase (light blue=straight sinus and proximal sigmoid sinus) to highlight arteriovenous shunting.
Dural Fistula — Clival branches of the MHT / Ascending Pharyngeal Artery
The clival arcade is beautifully seen in this case of a right sigmoid sinus fistula (black) supplied by the lateral tentorial arcade (yellow) from the ipsilateral right MHT
The contralateral, left MHT contributes to the same right lateral tentorial arcade (black) via multiple clival branches (purple). All images are in stereo
Detail of the same:
Trigeminal Artery — See dedicated cases of the Trigeminal Artery Page