Microsurgery of the third ventricle: Part I. Microsurgical anatomy.

The 3rd ventricle is one of the most surgically inaccessible areas in the brain. It is impossible to reach its cavity without incising some neural structures. Twenty-five cadaveric brains were examined in detail to evaluate the surgically important relationships of the walls of the 3rd ventricle. The routes through which the 3rd ventricle can be reached are (a) from above, through the foramen of Monro and the roof after entering the lateral ventricle through the corpus callosum or the cerebral cortex; (b) from anterior, through the lamina terminalis; (c) from below, through the floor if it has been stretched by tumor; and (d) from posterior, through the pineal region or from the posterior part of the lateral ventricle through the crus of the fornix. The posterior part of the circle of Willis and the basilar artery are intimately related to the floor, the anterior part of the circle of Willis and the anterior cerebral and anterior communicating arteries are related to the anterior wall, and the posterior cerebral artery supplies the posterior wall. The deep cerebral venous system is intimately related to the 3rd ventricle; the internal cerebral vein is related to the roof, and the basal vein is related to the floor. The junction of these veins with the great veins forms a formidable obstacle to the operative approach to the pineal gland and the posterior part of the 3rd ventricle.

Microsurgery of the third ventricle: Part 2. Operative approaches.

The operative approaches to the 3rd ventricle are divided on the basis of whether they are suitable for reaching the anterior or posterior part of the 3rd ventricle. The approaches suitable for lesions within or compressing the anterior portion of the 3rd ventricle are the trans-sphenoidal, subfrontal, frontotemporal, subtemporal, anterior transcallosal, and anterior transventricular. The approaches suitable for reaching the posterior portion of the 3rd ventricle are the posterior transcallosal, posterior transventricular, occipital transtentorial, and infratentorial supracerebellar. Considerations important in selecting one of these approaches are reviewed.

Microsurgical anatomy of the posterior inferior cerebellar artery.

Fifty cerebellar hemispheres from 25 adult cadavers were examined. The posterior inferior cerebellar artery (PICA), by definition, arose from the vertebral artery. The vertebral artery was present in 49 and the PICA was present in 42 of the 50 hemispheres. Forty-one of the 42 PICAs arose as a single trunk and 1 arose as a duplicate trunk. The PICA was divided into five segments: the anterior medullary segment lay on the front of the medulla; the lateral medullary segment coursed beside the medulla and extended to the origin of the glossopharyngeal, vagal, and accessory nerves; the tonsillomedullary segment coursed around the caudal half of the cerebellar tonsil; the telovelotonsillar segment coursed in the cleft between the tela choroidea and the inferior medullary velum rostrally and the superior pole of the cerebellar tonsil caudally; and the cortical segment was distributed to the cerebellar surface. Thirty-seven of the 42 PICAs bifurcated into a medial and a lateral trunk. The medial trunk supplied the vermis and the adjacent part of the hemisphere, and the lateral trunk supplied the cortical surface of the tonsil and the hemisphere. The PICA gave off perforating, choroidal, and cortical arteries. The cortical arteries were divided into vermian, tonsillar, and hemispheric groups. Sixteen of the 42 PICAs passed between the rootlets of the accessory nerve, 10 passed between the rootlets of the vagus nerve, 13 passed between the vagus and the accessory nerves, 2 coursed rostral to the glossopharyngeal nerve, and 1 passed between the glossopharyngeal and the vagus nerves.

Microsurgical anatomy of the superior cerebellar artery.

Fifty cerebellar hemispheres from 25 adult cadavers were examined. The superior cerebellar artery (SCA) was present in each of the 50 hemispheres. Forty-three SCAs arose as a single trunk, and 7 arose as duplicate trunks. One solitary trunk and the rostral trunk of one duplicate vessel arose from the posterior cerebral artery. The remainder arose from the basilar artery. The SCA was divided into four segments: the anterior pontomesencephalic segment lay below the oculomotor nerve; the lateral pontomesencephalic segment course; below the trochlear and above the trigeminal nerve; the cerebellomesencephalic segment coursed in the groove between the cerebellum and the upper brain stem; and the cortical segment was distributed to the cerebellar surface. The SCAs arising as a single trunk bifurcated into a rostral and a caudal trunk, corresponding to the runks formed by a duplicate origin. The rostral trunk supplied the medial and the caudal trunk supplied the lateral parts of the cerebellar cortex. The SCA gave off perforating, precerebellar, and cortical arteries. The perforating arteries penetrated the interpeduncular fossa, the cerebral peduncles, the junctions of the superior and middle cerebellar peduncles, and the colliculi. The precerebellar branches arose within the cerebellomesencephalic groove and supplied the adjoining parts of the cerebellum and brain stem. The cortical branches were divided into vermian, hemispheric, and marginal arteries. The 50 SACs had points of contact with 32 oculomotor, 46 trochlear, and 26 trigeminal nerves. (Neurosurgery, 6: 10--28, 1980)

The pretemporal approach to the interpeduncular and petroclival regions.

A pretemporal approach to the interpeduncular and petroclival regions is described. Through a frontotemporal craniotomy based very low in the middle fossa the temporal lobe is completely exposed. The Sylvian, carotid, chiasmatic, and lamina terminalis cisterns are widely opened. The arachnoid fibers between the uncus and the frontal lobe, as well as those binding the temporal lobe to the tentorial edge and to the oculomotor nerve are also separated. The bridging veins from the temporal pole to the spheno-parietal sinus are usually coagulated and sacrificed allowing for posterior displacement of the temporal lobe. The approach combines the advantages of both the classical pterional and subtemporal approaches providing unhindered exposure of the anterior portion of the tentorial incisura in dealing with vascular and tumoural lesions arising at the sellar, parasellar, and interpeduncular regions, and at the superior aspect of the petroclival region.

Anatomical and technical aspects of the contralateral approach for multiple aneurysms.

Microsurgery of multiple aneurysms is still a controversial subject. In order to avoid the risk of rebleeding and the consequent increase in morbidity in such cases all aneurysms or at least as many aneurysms as possible should be treated in the first operative procedure. To reach that goal aneurysms located on the contralateral side should also be considered for clipping during the first operation. Between 1984 and 1994 a series of 51 patients harboring multiple aneurysms of which 55 aneurysms were located on the contralateral side of the craniotomy were operated at our institution. No mortality or morbidity could be directly ascribed to the aneurysm that was clipped contralaterally. Based on that series we have described the anatomical features, technical aspects and surgical difficulties of approaching bilateral aneurysms through the same craniotomy.