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Panorama of Midline Structures from Cribriform Plates to the Tentorial Notch

Surgical Correlation

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Panorama of midline structures from cribriform plates to the tentorial notch. The cerebrum has been dissected away and the brainstem preserved in situ in this specimen. In the anterior cranial fossa, the cribriform plates of the ethmoid bone are separated by the crista galli, an attachment site for the falx cerebri. The left cribriform fossa is filled by the olfactory bulb receiving the neurofilaments of the olfactory nerve. Olfactory information from the bulb is transmitted along the olfactory tract to the olfactory cortex. Lateral to each cribriform plate are the orbital portions of the frontal bone. They form most of the anterior fossa floor and the roof of the orbits. The planum sphenoidale is an anterior midline portion of the body of the sphenoid that articulates with the cribriform plates and borders the chiasmatic sulcus posteriorly. It continues laterally as the lesser wings. The anterior petroclinoid ligaments extend from the anterior clinoid process of the lesser wing of sphenoid to the petrous apex of the temporal bone and represent the attached portion of the tentorium cerebelli (the posterior petroclinoid ligaments are its free edge). The remainder of the tentorium cerebelli is attached to the superior ridge of the petrous bone and to the transverse groove of the occipital bone. It divides the cranial cavity into supratentorial and infratentorial compartments. The tentorial notch or incisura is a U-shaped space that curves around the junction of the midbrain and pons to accommodate passage of the brainstem into the posterior fossa. The hyper-pigmented substantia nigra lies within the tegmentum of the midbrain posterior to the cerebral peduncles. Toward its dorsal surface in the midline is the narrow cerebral aqueduct that connects the third ventricle with the fourth ventricle. The oculomotor (CNIII) nerves can be seen leaving the ventral midbrain, passing through the interpeduncular fossa toward the lateral wall of the cavernous sinus. They penetrate the dura between the anterior and posterior petroclinoid ligaments lateral to and in front of the posterior clinoid processes. In their course they pass caudal to the posterior cerebral artery, between this and the superior cerebellar artery, both branches of the midline basilar artery. The trochlear (CNIV) nerves leave the dorsal surface of the midbrain and curve around the cerebral peduncles to gain the lateral wall of the cavernous sinus. They also pass between these two arteries and penetrate the dura between the free and attached edges of the tentorium cerebelli. At the intersection of the tentorium with the falx cerebri is the straight sinus. It receives at its anterior extremity the great cerebral vein (of Galen). This is a deep vein that drains most of the cerebrum. Ventral to the midbrain is the body of the sphenoid featuring the sella turcica, the midline depression containing the pituitary gland and distal pituitary stalk through the opening of the diaphragma sellae. The sella is bounded anteriorly by the tuberculum sellae and posteriorly by the dorsum sellae and its posterior clinoid processes. In this view, medial to the anterior clinoid processes are the optic nerves (CNII) emerging from the optic canals and the supraclinoid internal carotid arteries. The middle cranial fossa is the lateral depression between the lesser wing of the sphenoid and petrous portion of the temporal bone. (Image courtesy of PA Rubino)

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