Endoscopic anatomy of the cerebral aqueduct

What is known about the cerebral aqueduct is derived mainly from the legacy of classic histology and from the most recent advanced neuroimaging technologies. In fact, although this important structure is frequently glimpsed by neurosurgeons, only limited anatomic contributions have been added by microsurgery to its direct in vivo description. A review of our surgical experience in navigating the fourth ventricle prompted us to revisit the classical anatomic descriptions of the aqueduct and compare them using the novel perspective of neuroendoscopy.

We reviewed video recordings of 65 transaqueductal explorations of the fourth ventricle using flexible endoscopes, which were performed in our center to treat various pathological conditions. Forty-one patients were selected as being more informative for anatomic description. They include 21 patients with communicating normal pressure hydrocephalus, 6 patients with intraventricular hemorrhage, 5 patients with membranous obstruction of the foramen of Magendie, 5 patients with trapped fourth ventricle as evidenced after aqueductoplasty, 3 patients with colloid cysts, and 1 patient with craniopharyngioma with apparently normal aqueduct, which was navigated to aspirate small fragments of colloid and tiny clots.

Patients with normal-sized third ventricles confirmed the typical triangular shape of the aqueductal adytum, whereas all pathological aqueducts invariably had an oval contour. The posterior commissure, a faint trace of the median sulcus, and the rubral eminences were the structures invariably noticed. Five segments of the aqueduct were always identifiable: the adytum, first constriction, ampulla, second constriction, and posterior part or egressus.

Neuroendoscopy provides a novel perspective into the inner aqueductal wall and supplies an incomparable view of the intracanalicular anatomic structures.