Inferolateral Trunk (ILT):
The ILT arises as a single trunk or a collection of vessels from the lataral aspect of the cavernous carotid artery region. It usually supplies adjacent dura and cranial nerves and has extensive anastomoses with the extracranial circulation, particulary branches of the IMAX and middle meningeal artery as well as ophthalmic artery. It is a remnant of the primitive dorsal ophthalmic artery. The ILT and adult ophthalmic arteries are primary routes of ICA reconstitution following proximal ICA occlusion. The importance of understanding ECA-ICA collaterals of the ILT is paramount.
Figure 1: ILT and important anastomoses:
B) Recurrent branch of the ILT – courses along CN IV, and colalteralizes with branches of the MHT. Not rarely it annexes the territory of marginal tentorial (G) or lateral tentorial (F) arteries which more commonly come off the ILT (see ILT).
C) Anteromedial branch — a very important branch, this is a vestige of the primitive dorsal ophthalmic artery which in very early embryonic life supplied the orbit together with primitive ventral ophthalmic artery. This artery is hemodynamic balance with the recurrent meningeal branch (N) of the ophthalmic artery (M). Very rarely, when proximal ophthalmic (M) is absent, this branch (C) can reconstitute the ophthalmic artery (see ophthalmic artery section), although more commonly the middle meningeal artery fulfills this role through its opthalmic branch (K)
D) Artery to the foramen rotundum — another very important vessel supplying the nerve of the same foramen. It collateralizes with foramen rotundum branch of the IMAX (L), and is the primary route of ICA reconstitution via the IMAX
E) Foramen ovale branch — yet another important branch which supplies the appropriate foramen ovale nerve and collateralizes with the accessory meningeal artery (J) and also with carotid branch of the ascending pharyngeal artery (H) coming up through foramen ovale and cavernous branch (I) of the middle meningeal artery.
The checkered vessel anastomosing with the basilar artery (N) is the trigeminal artery, which sometimes originates from the region of the ILT.
Prominent ILT with reflux into accessory meningeal artery
Purple=ILT; Pink=accessory meningeal reflux; orange=acom; red=left frontopolar branch; yellow=left A1
Normally prominent artery of the foramen rotundum
In this patient, a normally prominent ILT (red) gives rise to the artery of the foramen rotundum (yellow), which supplies the roof of the nasopharynx, in combination with the also somewhat prominent Mandibulovidian Artery (pink) taking over the territory of the ascending pharyngeal in supply of the posterolateral nasopharynx (black). Notice the “down the barrel” view of the foramen rotundum artery within the foramen rotundum on the frontal native view (lower right).
ILT reconstitution of the ICA
The ILT, along with the ophthalmic artery, is a primary pathway of ICA reconstitution following proximal occlusion. Common routes include foramen rotundum branch, accessory and cavernous branches of the accessory and middle meningeal arteries.
ICA reconstitution following iatrogenic occlusion with coils (orange arrows) The ILT reconsitutes the ICA via sphenoid branches of the MMA (purple), foramen rotundum branch of the IMAX (yellow) and cavernous branches of the Accessory Meningeal (blue) arteries. The patient originally presented with a dural CC fistula. Possibly because the ILT vessels were already enlarged, they were relatively quickly recruited into ICA supply instead of the ophthalmic artery (green) which continues to fill its usual anterograde direction, highly unusual for an ICA occlusion. The coils in the cavernous sinus are also faintly visible in the region between the red and yellow arrows on the lateral projection (see below as well)
ICA occlusion with ILT and ophthalmic reconstitution. Cavernous branches of the MMA (red) participate in reconstitution of the inferolateral trunk region (brown) The sphenoidal branch (green, best seen on AP and foreshortened on the lateral) of the MMA (yellow) reconstitutes the ophthalmic artery (Blue)
Accessory meningeal reconstitution of the MCA territory via foramen ovale branch — right ICA is occluded at the origin. The ACOM is insufficient. Brisk reconstitution of the MCA territory is afforded via a the accessory meningeal artery inflow via the foramen ovale branches. Additional supply to the cavernous carotid was present via posterior clival branches of the MHT (see MHT). The orbital region is being reconstituted via the MMA.
Red=carotid; purple=extracranial MMA, pink=foramen spinosum; yellow=intracranial MMA; light blue=sphenoidal branch; dark blue=meningo-ophthalmic artery; green=accessory meningeal artery; white=foramen ovale branch of the ILT; brown=carotid stump
ILT flow reversal into ICA to support AVM. Lateral and AP projections demonstrating prominent supply of ILT via accessory meningeal and foramen rotundum branches. The ILT flow is revesed due to presence of a large right frontal AVM. Following embolization (lower right lateral ICA injection), the ILT is now visible off the ICA with normal anterograde flow.
Red=ICA. Purple=ILT. Dark Blue= rotundum. Light blue=foramen ovale branch to the accessory meningeal artery. Yellow=accessory meningeal.
Cavernous Origin of the Ophthalmic Artery — this rare disposition corresponds to persistence of embryonic dorsal ophthalmic artery, essentially representing an ILT origin of the ophthalmic. In the usual disposition, the anteromedial branch of the ILT (Figure 1, letter C) represents a vestige of the dorsal ophthalmic.
Persistence of dorsal ophthalmic artery. A — site of “classic” ophthalmic artery origin; B — dorsal ophthalmic artery; C — future ILT; D — recurrent meningeal branch of the ophthalmic artery; E — meningo-ophthalmic branch of the MMA
A vessel originates from the lateral cavernous portion of the left carotid artery corresponding to location of the ILT and enters the orbit (red arrows). The right ophthalmic artery origin (yellow) is normal. Average (left) and MIP (right) projections of the same case are seen below.
Similar case on angio of ophthalmic artery origin off the ILT
ILT and mandibulovidian reconstitution of IMAX territory
Foramen rotundum branch and other branches are commonly recruited for IMAX reconstituion of ICA in setting of proximal occlusion. The reverse may also take place following occlusion of the proximal IMAX, whereby the ILT feeds into the terminal IMAX in the pterygopalatine fossa. Typically, the facial artery is a much more robust candidate for reconstitution, so for ILT to become recruited the facial artery usually must be MIA as well. This is the case here, as the patient has had multiple surgeries for mandibular malocclusion and other issues. The upper left ECA injection demonstrates occlusion of the distal ECA trunk (pink) with reconsitution of the distal IMAX via two collateral branches (dark green and purple). The earlier (bottom left) and later (bottom right) images status post coiling of the ECA (bright green) demonstrate robust reconstitution of the pterygopalatine fossa IMAX (yellow) via foramen rotundum (light blue) and foramen ovale (red) branches of ILT (cream), as well as from the mandibulovidian artery (orange). The sphenopalatine (white) and descending palatine (blue) branches of the IMAX supply the palate and nasal mucosa and extend quite anteriorly on the later phase image. ALso note reconstituion of the Middle Meningeal Artery (brown) via retrograde flow thru the above-mentioned IMAX channels (purple and dark green) into the ECA above the coils (pink). Incidentally noted is presence of a prominent anterior meningeal artery (black) arising from the ophthalmic artery.