Subfrontal Translamina Terminalis Approach
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General Considerations and Indications for the Approach
The lamina terminalis is a thin membrane composed of gray matter, pia mater, and ependyma bordered superiorly by the anterior commissure, laterally by the cerebral hemispheres and inferiorly by the superior aspect of the optic chiasm. Embryologically, this lamina represents the most rostral end of the developing neural tube.
The subfrontal translamina terminalis approach uses the anterior wall of the third ventricle (lamina terminalis) to reach anterior lesions in this chamber. I use this approach rarely, mainly for large predominately solid craniopharyngiomas and hypothalamic hamartomas. Cystic craniopharyngiomas are ideally exposed via the transnasal transtuberculum route.
The subfrontal approach for a solid third ventricular craniopharyngioma requires a modified orbitozygomatic craniotomy, so an inferior-to-superior subfrontal operative trajectory facilitates handling of the superior pole of the tumor without aggressive retraction of the basal frontal lobe.
The subfrontal translamina terminalis approach is a restricted, nonflexible operative corridor that cannot be safely expanded. Gross total tumor resection can be problematic. The anterior interhemispheric modification of this approach may provide more extended operative space but is not minimally disruptive.
The manipulations required through this narrow corridor often lead to cognitive decline, most likely because of blind dealings with the ventricular wall. Despite use of an orbitozygomatic craniotomy, a fair amount of retraction on the frontal lobe is necessary.
For a specific discussion of the preoperative considerations for third ventricular tumors, see the Principles of Intraventricular Surgery chapter.
Preoperative endocrinological and ophthalmological evaluations are necessary. The lamina terminalis should be affected by the tumor and the optic apparatus should not be covering the anterior and inferior poles of the tumor. The floor of the ventricle should also be affected by the tumor. An intact third ventricular floor is a contraindication for the use of this route and supports the use of the transcallosal transforaminal transvenous transchoroidal approach.
The anatomy of the lamina terminalis is summarized in the following images.
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SUBFRONTAL TRANSLAMINA TERMINALIS APPROACH VIA AN ORBITOZYGOMATIC CRANIOTOMY
This approach is especially favorable if the solid tumor extends through the lamina terminalis and has a small suprasellar component. Tumors with primarily suprasellar components are resected through the endoscopic transnasal transsphenoidal translamina terminalis approach.
This subfrontal translamina terminalis approach offers the advantage of providing excellent visualization of the lamina terminalis, optic nerves, optic chiasm, bilateral internal carotid arteries, anterior communicating artery complex, bilateral A2 segments, posterior communicating arteries, associated perforating branches, and the pituitary stalk.
The use of dynamic retraction and wide arachnoidal dissection over bilateral optic nerves are necessary in reaching the lamina terminalis. The vector of retraction is parallel to the ipsilateral optic nerve.
If the tumor reaches into the sella, the intrasellar portion of the tumor may be removed via the corridor between the optic nerves. However, I do not recommend this maneuver because of its associated morbidity that results from the blind manipulation of the optic nerves and their perforating vessels. The prefix chiasm can limit this working space.
For a detailed discussion of recommendations for postoperative care of patients with ventricular tumors, see the Principles of Intraventricular Surgery chapter.
Pearls and Pitfalls
- The subfrontal translamina terminalis approach is restrictive and should be used in the case of small tumors that are not amenable to its endoscopic transnasal counterpart. Gross total resection of large tumors is problematic and not usually feasible without undue retraction on the surrounding normal neurovascular structures.
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