• Hugo Leonardo Doria-Netto, CamposChristiane Monteiro de SiqueiraCMSDivision of Neuroradiology, Hospital Beneficência Portuguesa de São Paulo, São Paulo, Brazil., Victor Hugo Rocha Marussi, José Maria Campos-Filho, Jean Faber, Michael T Lawton, and Feres E A Chaddad-Neto.
• Department of Neurology and Neurosurgery, Universidade Federal de São Paulo (Unifesp), São Paulo, São Paulo, Brazil; Division of Neurosurgery, Hospital Beneficência Portuguesa de São Paulo, São Paulo, Brazil.
• World Neurosurg. 2022 Nov 1; 167: e475e506e475-e506.

ObjectiveTo evaluate the relationship between the oculomotor nerve (CNIII) and the internal carotid artery (ICA) as a new anatomic-radiologic landmark for distinguishing the exact location of a paraclinoid intracranial aneurysm (IA).MethodsMicroanatomic dissections were performed in 20 cavernous sinuses to evaluate the ICA paraclinoid region. Based on anatomic observations, a new magnetic resonance (MRI) protocol to classify paraclinoid aneurysms was proposed. MRI of 42 IAs from 34 patients was independently analyzed and classified as intracavernous, extracavernous, or transitional by 2 neuroradiologists. To validate the proposed MRI protocol, each IA was classified by a three-dimensionally (3D) printed biomodel and agreement with the radiologic classifications was evaluated. Of 42 IAs, 23 undergoing microsurgeries were also classified by direct visualization.ResultsWe observed that the true cavernous sinus roof is defined by the carotid-oculomotor membrane, which has an intimate relationship with the intersection between the superior limit of the CNIII and the ICA. Based on this intersection, all 42 IAs were radiologically classified and agreement with the 3D printed biomodels was observed in 95% IAs. Concordance tests showed a statistically significant (P < 0.05) agreement between the classifications. All 23 IAs treated had the radiologic and 3D biomodel classification confirmed.ConclusionsThe intersection between the ICA and the CNIII, which crosses it transversely in its entire diameter, is a reliable anatomic-radiologic landmark to correctly classify paraclinoid aneurysms. Through a new MRI protocol, it is possible to radiologically identify this intersection and to easily distinguish the intracavernous and extracavernous ICA paraclinoid aneurysms.Copyright © 2022 Elsevier Inc. All rights reserved.

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