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Ali Tayebi Meybodi, Leandro Borba Moreira, Andrew S. Little, Michael T. Lawton, and Mark C. Preul

OBJECTIVE

Endoscopic endonasal approaches (EEAs) are increasingly being incorporated into the neurosurgeon’s armamentarium for treatment of various pathologies, including paraclinoid aneurysms. However, few anatomical assessments have been performed on the use of EEA for this purpose. The aim of the present study was to provide a comprehensive anatomical assessment of the EEA for the treatment of paraclinoid aneurysms.

METHODS

Five cadaveric heads underwent an endonasal transplanum-transtuberculum approach to expose the paraclinoid area. The feasibility of obtaining proximal and distal internal carotid artery (ICA) control as well as the topographic location of the origin of the ophthalmic artery (OphA) relative to dural landmarks were assessed. Limitations of the EEA in exposing the supraclinoid ICA were also recorded to identify favorable paraclinoid ICA aneurysm projections for EEA.

RESULTS

The extracavernous paraclival and clinoidal ICAs were favorable segments for establishing proximal control. Clipping the extracavernous ICA risked injury to the trigeminal and abducens nerves, whereas clipping the clinoidal segment put the oculomotor nerve at risk. The OphA origin was found within 4 mm of the medial opticocarotid point on a line connecting the midtubercular recess point to the medial vertex of the lateral opticocarotid recess. An average 7.2-mm length of the supraclinoid ICA could be safely clipped for distal control. Assessments showed that small superiorly or medially projecting aneurysms were favorable candidates for clipping via EEA.

CONCLUSIONS

When used for paraclinoid aneurysms, the EEA carries certain risks to adjacent neurovascular structures during proximal control, dural opening, and distal control. While some authors have promoted this approach as feasible, this work demonstrates that it has significant limitations and may only be appropriate in highly selected cases that are not amenable to coiling or clipping. Further clinical experience with this approach helps to delineate its risks and benefits.

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Ali Tayebi Meybodi, Andrew S. Little, Vera Vigo, Arnau Benet, Sofia Kakaizada, and Michael T. Lawton

OBJECTIVE

The transpterygoid extension of the endoscopic endonasal approach provides exposure of the petrous apex, Meckel’s cave, paraclival area, and the infratemporal fossa. Safe and efficient localization of the lacerum segment of the internal carotid artery (ICA) is a crucial part of such exposure. The aim of this study is to introduce a novel landmark for localization of the lacerum ICA.

METHODS

Ten cadaveric heads were prepared for transnasal endoscopic dissection. The floor of the sphenoid sinus was drilled to expose an extension of the pharyngobasilar fascia between the sphenoid floor and the pterygoid process (the pterygoclival ligament). Several features of the pterygoclival ligament were assessed. In addition, 31 dry skulls were studied to assess features of the bony groove harboring the pterygoclival ligament.

RESULTS

The pterygoclival ligament was identified bilaterally during drilling of the sphenoid floor in all specimens. The ligament started a few millimeters posterior to the posterior end of the vomer alae and invariably extended posterolaterally and superiorly to blend into the fibrous tissue around the lacerum ICA. The mean length of the ligament was 10.5 ± 1.7 mm. The mean distance between the anterior end of the ligament and midline was 5.2 ± 1.2 mm. The mean distance between the posterior end of the ligament and midline was 12.3 ± 1.4 mm. The bony pterygoclival groove was identified at the confluence of the vomer, pterygoid process of the sphenoid, and basilar part of the occipital bone, running from posterolateral to anteromedial. The mean length of the groove was 7.7 ± 1.8 mm. Its posterolateral end faced the anteromedial aspect of the foramen lacerum medial to the posterior end of the vidian canal. A clinical case illustration is also provided.

CONCLUSIONS

The pterygoclival ligament is a consistent landmark for localization of the lacerum ICA. It may be used as an adjunct or alternative to the vidian nerve to localize the ICA during endoscopic endonasal surgery.