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Tentorial, Suboccipital, and Petrosal Cerebellar Surfaces

Surgical Correlation

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A, The tentorial surface faces the lower surface of the tentorium. The anterior vermis is the most superior part of the tentorial surface. This surface slopes downward to its posterior and lateral margins. The vermian subdivisions of this surface are superior to their corresponding hemispheric parts. The classical nomenclature applied to the vermian and hemispheric subdivisions of the tentorial surface is listed on the right, and our simplified nomenclature is listed on the left. The culmen and quadrangular lobules correspond to the anterior part of the tentorial surface, and the declive, simple lobules, and part of the superior semilunar lobules correspond to the posterior part of the tentorial surface. The fissure separating the tentorial surface into anterior and posterior parts is referred to as the tentorial fissure in our nomenclature, but is the primary fissure in older nomenclature. This fissure separates the hemispheric surface between the quadrangular and simple lobules and the vermis between the declive and culmen. The anterior part of the superior surface of the cerebellum surrounds the posterior half of the midbrain to form the cerebellomesencephalic fissure. B, Suboccipital surface. The suboccipital surface is located below and between the sigmoid and lateral sinuses and is the surface that is exposed in a wide bilateral suboccipital craniectomy. The classical nomenclature applied to this surface is shown on the right, and our simplified nomenclature is on the left. The vermis sits in a large median depression, the posterior cerebellar incisura, between the cerebellar hemispheres. According to classical nomenclature, the portions of the vermis within the incisura from above to below are the folium, tuber, pyramid, and uvula. The parts of the hemispheric surface from above to below are the superior and inferior semilunar and biventral lobules and the tonsils. These lobules extend beyond the suboccipital surface to the other surfaces of the cerebellum. The prebiventral fissures between the inferior semilunar and the biventral lobules separate the hemispheres into superior and inferior parts, and the prepyramidal fissure between the pyramid and tuber separates the vermis into superior and inferior parts. We refer to the union of the prebiventral and the prepyramidal fissures that divide the suboccipital surface into superior and inferior parts as he suboccipital fissure. From below to above the corresponding vermian and hemispheric parts are the uvula and the tonsils, the pyramid and the biventral lobules, the tuber and inferior semilunar lobules, and the folium and the superior semilunar lobules. The petrosal (horizontal) fissure, the most prominent fissure on the petrosal surface, extends onto the suboccipital surface and divides the superior half of the suboccipital surface between the superior and inferior semilunar lobules. The cerebellomedullary fissure extends superiorly between the cerebellum and medulla. C, Petrosal surface. The petrosal surface faces forward toward the petrous temporal bone and is the surface that is retracted to surgically expose the cerebellopontine angle. The classical nomenclature applied to this surface is shown on the right, and our simplified nomenclature is on the left. The petrosal fissure divides the petrosal surface into superior and inferior parts. The superior part is formed by the quadrangular, simple, and a small part of the superior semilunar lobules. The inferior part is formed by the inferior semilunar and biventral lobules and the tonsil. The cerebellopontine fissures are V-shaped fissures formed where the cerebellum wraps around the pons and the middle cerebellar peduncles. These fissures have a superior and an inferior limb, which meet at a lateral apex. The petrosal fissure extends laterally from the apex of the cerebellopontine fissures. (Images courtesy of AL Rhoton, Jr.)

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