Atlas of neurosurgery basic approaches to cranial Meyer

Figure 12-14. Step 2. A, Illustrated here is the typical appearance of the right foramen of Monro as visualized through an endoscope. Usually, the foramen of Monro is enlarged because of the fornix being stretched. The typical intraventricular landmarks visualized include the medial septal vein, choroidal plexus, thalamostriate vein, and lateral anterior caudate vein. It is important not to traumatize the fornix as the endoscope passes through the foramen of Monro. Most endoscopes have a side port that can be used for irrigation. Irrigating through the scope as it is inserted through the foramen will gently push the fornix out of harm’s way. Step 3. B, As the scope is inserted through the foramen of Monro, the mammillary bodies become more visible. The point of puncture is anterior to the mammillary bodies in the tuber cinereum. Looking through the endoscope, anterior is the dorsum sellae and clivus. If the tuber cinereum is thin, the outline of either the basilar or the posterior cerebral artery may be seen. Step 4. C, There are several techniques for puncturing the tuber cinereum. For example, the endoscope itself can be used. More sophisticated scopes have a side port that allows passage of a dilating balloon to enlarge the third ventriculostomy. Often, there is slight bleeding, which will stop with irrigation. D, The endoscope can be inserted deeper to better visualize the basilar artery. Usually, there are strands of arachnoid between the clivus and the basilar artery. The surgeon should not attempt to cut or to lyse these arachnoid trabeculations. If the patient has a functioning shunt, it is important to ligate it to make sure that the flow of cerebrospinal fluid is directed through the third ventriculostomy to increase the likelihood of patency.

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