=====Posterior clinoid process meningioma=====

[[Posterior clinoid process]] (PCP) [[intracranial meningioma]]s are extremely rare lesions and comprise about 0.7% of [[central skull base meningioma]]s

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
((Shukla D, Gangadharan J, Kakati A, Devi BI. Posterior clinoid process
meningioma. Clin Neurol Neurosurg. 2013 Aug;115(8):1517-9. doi:
10.1016/j.clineuro.2012.12.007. Epub 2013 Jan 11. PubMed PMID: 23313105.
)).
====Classification====
Clinical and radiological features or characteristics of [[posterior clinoid process]] (PCP) meningiomas have rarely been described because of their extreme scarcity and terminological confusion. 

These tumors are often referred to as “[[dorsum sellae]]” or "upper [[clivus meningioma]]s"
((Dolenc VV, Skrap M, Sustersic J, Skrbec M, Morina A. A transcavernous-transsellar approach to the basilar tip aneurysms. Br J Neurosurg. 1987;1:251–9.))
((Geng SM, Zhang JT, Zhang LW, Wu Z, Wang ZC. Optimal microsurgical treatment of dorsum sellae meningioma. Chin Med J (Engl) 2009;122:1857–61.))
((Nakamura M, Samii M. Surgical management of a meningioma in the retrosellar region. Acta Neurochir (Wien) 2003;145:215–9.))
((Shukla D, Gangadharan J, Kakati A, Devi BI. Posterior clinoid process
meningioma. Clin Neurol Neurosurg. 2013 Aug;115(8):1517-9. doi:
10.1016/j.clineuro.2012.12.007. Epub 2013 Jan 11. PubMed PMID: 23313105.
)).

Geng et al. subdivided the [[dorsum sellae meningioma]]s 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
((Geng SM, Zhang JT, Zhang LW, Wu Z, Wang ZC. Optimal microsurgical treatment of dorsum sellae meningioma. Chin Med J (Engl) 2009;122:1857–61.))
((Nakamura M, Samii M. Surgical management of a meningioma in the retrosellar region. Acta Neurochir (Wien) 2003;145:215–9.))
((Shukla D, Gangadharan J, Kakati A, Devi BI. Posterior clinoid process
meningioma. Clin Neurol Neurosurg. 2013 Aug;115(8):1517-9. doi:
10.1016/j.clineuro.2012.12.007. Epub 2013 Jan 11. PubMed PMID: 23313105.
)).
----
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 meningioma]]s.

Eccentrically placed meningiomas centered on the PCP are true PCP meningiomas
((Sodhi HB, Singla N, Gupta SK. Posterior clinoid meningioma: A case report with
discussion on terminology and surgical approach. Surg Neurol Int. 2015 Feb
11;6:21. doi: 10.4103/2152-7806.151261. eCollection 2015. PubMed PMID: 25722927; 
PubMed Central PMCID: PMC4338485.
)).

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
((Takase H, Kawasaki T, Tateishi K, Yokoyama TA, Murata H, Kawahara N.
Characteristics and surgical strategies for posterior clinoid process meningioma:
two case reports and review of the literature. Neurosurg Rev. 2016 Aug 24. [Epub 
ahead of print] PubMed PMID: 27553846.
)).

====Differential diagnosis====
Hongo et al., report a case of an [[osteochondroma]] in the posterior clinoid process that occurred in a 43-year-old man with [[trochlear nerve palsy]]. Although the potential preoperative diagnoses based on computed tomography and magnetic resonance imaging included other intracranial tumors such as calcified meningioma, thallium-201 single-photon emission computed tomography effectively differentiated osteochondroma from those possibilities
((Hongo H, Oya S, Abe A, Matsui T. Solitary Osteochondroma of the Skull Base: A 
Case Report and Literature Review. J Neurol Surg Rep. 2015 Jul;76(1):e13-7. doi: 
10.1055/s-0034-1387189. Epub 2015 Mar 2. PubMed PMID: 26251790; PubMed Central
PMCID: PMC4520987.
)).

====Treatment=====
In close proximity to these lesions are the perforators from the [[internal carotid artery]] (ICA) and the [[oculomotor nerve]], which need to be considered while deciding the appropriate surgical [[approach]].

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
((Sodhi HB, Singla N, Gupta SK. Posterior clinoid meningioma: A case report with
discussion on terminology and surgical approach. Surg Neurol Int. 2015 Feb
11;6:21. doi: 10.4103/2152-7806.151261. eCollection 2015. PubMed PMID: 25722927; 
PubMed Central PMCID: PMC4338485.
)).
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
((Takase H, Kawasaki T, Tateishi K, Yokoyama TA, Murata H, Kawahara N.
Characteristics and surgical strategies for posterior clinoid process meningioma:
two case reports and review of the literature. Neurosurg Rev. 2016 Aug 24. [Epub 
ahead of print] PubMed PMID: 27553846.
)).

====Approaches====
Various surgical approaches have been described to approach the PCP to minimize complications, and to improve the extent of resection. 

These include the extradural trancavernous-transellar approach described by Dolenc
((Dolenc VV, Skrap M, Sustersic J, Skrbec M, Morina A. A transcavernous-transsellar approach to the basilar tip aneurysms. Br J Neurosurg. 1987;1:251–9.)).

A frontotemporal or pterional approach, presigmoid transpetrosal approach, and a transzygomatic subtemporal approach
((Shukla D, Gangadharan J, Kakati A, Devi BI. Posterior clinoid process
meningioma. Clin Neurol Neurosurg. 2013 Aug;115(8):1517-9. doi:
10.1016/j.clineuro.2012.12.007. Epub 2013 Jan 11. PubMed PMID: 23313105.
)).

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
((Nakamura M, Samii M. Surgical management of a meningioma in the retrosellar region. Acta Neurochir (Wien) 2003;145:215–9.))
((Shukla D, Gangadharan J, Kakati A, Devi BI. Posterior clinoid process
meningioma. Clin Neurol Neurosurg. 2013 Aug;115(8):1517-9. doi:
10.1016/j.clineuro.2012.12.007. Epub 2013 Jan 11. PubMed PMID: 23313105.
)).

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
((Dolenc VV, Skrap M, Sustersic J, Skrbec M, Morina A. A transcavernous-transsellar approach to the basilar tip aneurysms. Br J Neurosurg. 1987;1:251–9.)).
The transcavernous approach described by Dolenc is also potentially hazardous for the cranial nerves and the ICA
((Dolenc VV, Skrap M, Sustersic J, Skrbec M, Morina A. A transcavernous-transsellar approach to the basilar tip aneurysms. Br J Neurosurg. 1987;1:251–9.)).

====Complications====
Complication with the perforators is also hazardous of these challenging surgeries than [[anterior clinoid region meningioma]]s for their specific neuroanatomical structures and might not be feasible to avoid even with additional techniques and critical monitoring. A combination and multi-staged-surgical approach can be options of tailor-made surgical strategy in cases with tumor adhesion to the perforators
((Takase H, Kawasaki T, Tateishi K, Yokoyama TA, Murata H, Kawahara N.
Characteristics and surgical strategies for posterior clinoid process meningioma:
two case reports and review of the literature. Neurosurg Rev. 2016 Aug 24. [Epub 
ahead of print] PubMed PMID: 27553846.
)).
====Case reports====
The tumor described by Nakamura et al. was anteriorly placed, arising from the upper clivus and should be labeled as dorsum sellae or upper clival meningioma
((Nakamura M, Samii M. Surgical management of a meningioma in the retrosellar region. Acta Neurochir (Wien) 2003;145:215–9. )).

Geng et al. discussed eight cases of dorsum sellae meningiomas (types 1 and 2) but did not mention the exact site of origin
((Geng SM, Zhang JT, Zhang LW, Wu Z, Wang ZC. Optimal microsurgical treatment of dorsum sellae meningioma. Chin Med J (Engl) 2009;122:1857–61.))
((Nakamura M, Samii M. Surgical management of a meningioma in the retrosellar region. Acta Neurochir (Wien) 2003;145:215–9.))
((Shukla D, Gangadharan J, Kakati A, Devi BI. Posterior clinoid process
meningioma. Clin Neurol Neurosurg. 2013 Aug;115(8):1517-9. doi:
10.1016/j.clineuro.2012.12.007. Epub 2013 Jan 11. PubMed PMID: 23313105.
)).


===2016===
Takase et al., report two surgical cases of PCP meningioma and discuss the appropriate assessment of preoperative features and surgical strategies with review of the literature
((Takase H, Kawasaki T, Tateishi K, Yokoyama TA, Murata H, Kawahara N.
Characteristics and surgical strategies for posterior clinoid process meningioma:
two case reports and review of the literature. Neurosurg Rev. 2016 Aug 24. [Epub 
ahead of print] PubMed PMID: 27553846.
)).

===2015===
Sodhi et al., describe a basal frontotemporo-orbito-zygomatic approach with splitting of the sylvian fissure to resect an eccentrically placed PCP meningioma.

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
((Sodhi HB, Singla N, Gupta SK. Posterior clinoid meningioma: A case report with
discussion on terminology and surgical approach. Surg Neurol Int. 2015 Feb
11;6:21. doi: 10.4103/2152-7806.151261. eCollection 2015. PubMed PMID: 25722927; 
PubMed Central PMCID: PMC4338485.
)).

===2013===
Shukla et al. reported a patient as posterior clinoid meningioma, which was eccentric and centered over the PCP
((Shukla D, Gangadharan J, Kakati A, Devi BI. Posterior clinoid process
meningioma. Clin Neurol Neurosurg. 2013 Aug;115(8):1517-9. doi:
10.1016/j.clineuro.2012.12.007. Epub 2013 Jan 11. PubMed PMID: 23313105.
)).