Posterior clinoid process (PCP) intracranial meningiomas are extremely rare lesions and comprise about 0.7% of central skull base meningiomas
Meningiomas arising from the PCP can compress the pituitary stalk anteriorly, the oculomotor nerve laterally or infero-laterally and encase the C1-C2 segment of the internal carotid artery (ICA) or its perforators and branches 1).
Classification
These tumors are often referred to as “dorsum sellae” or “upper clivus meningiomas” 2) 3) 4) 5).
Geng et al. subdivided the dorsum sellae meningiomas into two groups
Type 1 (dorsum sellae, inferior third ventricle type)
Type 2 (dorsum sellae, third ventricular type), depending upon the site and direction of growth 6) 7) 8).
Lesions in this region are primarily of two anatomic types:
Centrally placed meningiomas located between the two PCPs and arising from the dorsum sellae or upper clival region – which should be referred to as dorsum sellae meningioma or upper clivus meningiomas.
Eccentrically placed meningiomas centered on the PCP are true PCP meningiomas 9).
Takase et al., suggests that PCP meningioma may be characterized by the anterior displacement of internal carotid artery, and infero-laterally shifted posterior communicating artery, and homonymous hemianopsia, a distinctive clinical feature 10).
Differential diagnosis
Treatment
Strategies in the surgical intervention have not been well established. Moreover, the proximity to important neurovascular structures, including optic chiasm, internal carotid artery (ICA), pituitary stalk, and oculomotor nerve, can be difficult to predict preoperatively, making their surgical excision more challenging.
Differentiation between the dorsum sellae/upper clival meningiomas and the PCP meningiomas may have important implications in selecting the surgical approach 12). One of the key issues in PCP meningioma surgery is preservation of the optic nerve. Unlocking the optic nerve by anterior clinoidectomy and dissection, the falciform ligament is the important step to preserve vision for larger tumors 13).
Approaches
These include the extradural trancavernous-transellar approach described by Dolenc 14).
A frontotemporal or pterional approach, presigmoid transpetrosal approach, and a transzygomatic subtemporal approach 15).
In the frontotemporal and pterional approach, there is direct access to the tumor through the optico-carotid and carotico-oculomotor corridors, but the perforators, which are pushed anteriorly by the tumor, are at risk of injury or vasospasm. A two stage approach, combining retrosigmoid suboccipital corridor to devascularize the tumor, followed by total excision of the tumor by frontotemporal route, has also been described 16) 17).
The transzygomatic subtemporal approach is anatomically a good technique as it allows the dural attachment of the tumor to be coagulated first, followed by piecemeal tumor excision. However, temporal lobe retraction may be hazardous and occasional venous infarcts have been reported 18). The transcavernous approach described by Dolenc is also potentially hazardous for the cranial nerves and the ICA 19).
Complications
Case reports
Geng et al. discussed eight cases of dorsum sellae meningiomas (types 1 and 2) but did not mention the exact site of origin 22) 23) 24).
2016
2015
The approach allowed access through the carotico-optic corridor, and between the carotid artery and the oculomotor nerve, as well as the anterior subtemporal approach. This provided an additional surgical trajectory allowing direct access to the PCP posterior to the perforating vessels without temporal lobe retraction.
A basal frontotemporo-orbito-zygomatic approach with splitting of the sylvian fissure is a safe approach to resect an eccentrically placed PCP meningioma 26).