The superior fovea triangle approach: a novel safe entry zone to the brainstem

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The authors describe a safe entry zone, the superior fovea triangle, on the floor of the fourth ventricle for resection of deep dorsal pontine lesions at the level of the facial colliculus. Clinical data from a patient undergoing a suboccipital telovelar transsuperior fovea triangle approach to a deep pontine cavernous malformation were reviewed and supplemented with 6 formalin-fixed adult human brainstem and 2 silicone-injected adult human cadaveric heads using the fiber dissection technique to illustrate the utility of this novel safe entry zone. The superior fovea has a triangular shape that is an important landmark for the motor nucleus of the trigeminal, abducens, and facial nerves. The inferior half of the superior fovea triangle may be incised to remove deep dorsal pontine lesions through the floor of the fourth ventricle. The superior fovea triangle may be used as a safe entry zone for dorsally located lesions at the level of the facial colliculus.

ABBREVIATIONS CN = cranial nerve.

Article Information

Correspondence Robert F. Spetzler, c/o Neuroscience Publications, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, 350 W Thomas Rd., Phoenix, AZ 85013. email: neuropub@dignityhealth.org.

INCLUDE WHEN CITING Published online December 23, 2016; DOI: 10.3171/2016.8.JNS16947.

Drs. Yagmurlu and Kalani contributed equally to this work.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

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    Superior fovea triangle. A: The sulcus limitans, a lateral sulcus, deepens at 2 points to form dimples called fovea. The superior fovea is located lateral to the facial colliculus, and the inferior fovea is located lateral to the hypoglossal triangle. B: The facial colliculus is formed by the abducens nucleus and the intrapontine segment of the facial nerve. The superior cerebellar peduncle forms the superior half of the lateral wall of the fourth ventricle, and the inferior cerebellar peduncle forms the inferior half of the lateral wall of the fourth ventricle. C: The suprafacial approach, above the facial colliculus, and the infrafacial approach, below the facial colliculus, are used for dorsal pontine lesions. The trigeminal motor and main sensory nuclei (green circle) are located above the upper level of the facial colliculus and the most lateral point of the fourth ventricle. D: The sulcus limitans deepens lateral to the facial colliculus, which is called the superior fovea. The superior fovea has a triangular shape (green dashed triangle): its superolateral edge is formed by the superior cerebellar peduncle, its inferolateral edge is formed by the vestibular area, and its medial edge is formed by the sulcus limitans. The trigeminal motor nuclei (yellow circle) are located deep to the superolateral edge of the superior fovea triangle, and the apex of the triangle is located at the same transverse level as the upper edge of the facial colliculus (blue dashed line). Cer. Ped. = cerebellar peduncle; Coll. = colliculus; Hypo = hypoglossal; Inf. = inferior; Med. Sulc. = median sulcus; Nucl. = nucleus; Sulc. Lim. = sulcus limitans; Sup. = superior; Vest. = vestibular. Dissections prepared by Kaan Yagmurlu, MD. Reproduced with permission from the Rhoton Collection (http://rhoton.ineurodb.org), CC BY-NC-SA 4.0 (http://creativecommons.org/licenses/by-nc-sa/4.0).

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    Possibilities of displacement (arrow) of the facial colliculus according to different lesion locations (starburst). A: A lesion located rostral to the axial level of the facial colliculus pushes the facial colliculus caudally. B: A lesion located caudal to the axial level of the facial colliculus displaces the facial colliculus rostrally. C: A lesion located at the same axial level as the facial colliculus and close to the midline displaces the facial colliculus laterally toward the superior fovea. D: A lesion located at the same axial level as the facial colliculus and laterally displaces the facial colliculus medially. Coll. = colliculus. Dissections prepared by Kaan Yagmurlu, MD. Reproduced with permission from the Rhoton Collection (http://rhoton.ineurodb.org), CC BY-NC-SA 4.0 (http://creativecommons.org/licenses/by-nc-sa/4.0).

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    Midline suboccipital telovelar approach. A and B: The suboccipital midline craniotomy and dural opening (A) expose the dorsal medulla and the cerebellar tonsils (B). C: The telovelar junction is exposed by opening the sulcus between the uvula and the cerebellar tonsil. The telovelar junction is incised (green dashed line) to expose the floor of the fourth ventricle. D: The facial colliculus is a prominence on the fourth ventricle, and the inferior half of the superior fovea triangle is incised (red dotted line). Coll. = colliculus; Junct. = junction. Panel A: Copyright Barrow Neurological Institute, Phoenix, Arizona. Published with permission. Panels B–D: Dissections prepared by Kaan Yagmurlu, MD. Reproduced with permission from the Rhoton Collection (http://rhoton.ineurodb.org), CC BY-NC-SA 4.0 (http://creativecommons.org/licenses/by-nc-sa/4.0).

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    A 68-year-old male patient presented with acute-onset facial paralysis. A–C: Preoperative axial T1-weighted (A), sagittal T1-weighted (B), and axial T2-weighted (C) MRI studies demonstrating a dorsal pontine cavernous malformation at the level of the facial colliculus. The lesion was approached using a midline suboccipital telovelar approach. The opening in the brainstem was placed laterally at the superior fovea. D and E: Postoperative axial T1-weighted (D) and sagittal T2-weighted (E) MRI studies demonstrating complete resection of the lesion.

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