Case Archives Petroclival Meningioma MHT and ILT access

In collaboration with Dr. Chandra Sen, Dr. David Gordon, and Dr. Eytan Raz

The dominant supply of a meningioma is determined by its original location. With continued growth, meningiomas will recruit additional sources, closely corresponding to their location and embryologic disposition of the host. For example, a sphenoid wing meningioma may receive dominant supply from the ILT, the middle meningeal, or accessory meningeal arteries, depending on which vessel was the pre-morbid dominant supplier to the area of subsequent tumor origin. In a patient with recurrent meningeal variant, for example, dominant supply will arise from the ophthalmic artery.

When it comes to petroclival meningiomas, it is thus reasonable to expect multiple sources of supply. The ascending pharyngeal artery, particularly the jugular branch of the neuromeningeal trunk, will nearly always be contributing, as will the ipsilateral ILT or MHT. Large petroclival meningiomas will often have bilateral MHT or ILT supply — usually the ipsilateral branch is the ILT, and contralateral is the MHT (because MHT has medial / midline territory, while ILT is by definition inferolateral).

The notion that both MHT and ILT are always off limits for tumor embolization is not in agreement with the ultimate goal of effective devascularization. First, the territory these branches supply is no more “dangerous” than other branches which are routinely subjected to particle embolization. In fact, the petrous branch of the MMA, with its supply of the facial nerve arcade and petrosal nerve, or the neuromeningeal trunk of the ascending pharyngeal artery, which supplies CN 9, 10, and 11 (jugular division) and 12 (hypoglossal division), are as eloquent as MHT or ILT supply to CN III, IV, V, or VI. Second, it is just as easy, and perhaps easier, to get into “dangerous anastomoses” trouble with MMA or AP (vertebral, carotid, ophthalmic connections) as it is with ILT or MHT. In a certain sense, dangerous anastomoses during ILT and MHT are actually easier to monitor — basically watching for ipsilateral carotid reflux, and contralateral carotid with MHT (inferior clival / hypophyseal branches, vestiges of the primitive maxillary artery) and ophthalmic branches during ILT embo (monitoring for anything going ventral).

If a tumor has extensive ILT or MHT supply, and if the operator decides not to proceed with embolization of these pedicles, it is probably best to consider as to whether it makes sense to embolize the tumor at all, since a very partial embolization accomplishes no medically useful purpose. In our experience, the incidence of cranial neuropathy with particle embolization of these trunks is no higher than with takedown of the ascending pharyngeal — meaning less than 5%. Whether or not this kind of risk makes sense depends on tumor location and overall treatment goals. Again, for embolization to have an effective role it must be considered as part of an overall treatment package — the more risk is assumed by embolization the less risk is taken during surgery. Where that balance should be depends on mutually agreed upon pre-procedural goals.

From a technical perspective, the MHT is generally easier to catheterize than the ILT, because the former is located at the posterior genu and is thus easier to engage,whereas the latter usually comes off the lateral wall and curves posteriorly, making it doubly difficult to catheterize. Small particles can be used with nearly all microcatheters.

This patient presented with progressive imbalance; asymptomatic hearing impairment was noted on subsequent workup. Notice a vessel running through the tumor (red arrow, T2 image — this is the AICA)