10 Transsellar Transdorsal Approach

10.1055/b-0039-172572

10 Transsellar Transdorsal Approach

Marco Ferrari, Marco Ravanelli, Francesco Belotti, Francesco Doglietto

The transdorsal approach constitutes the transnasal pathway through the upper third of the clivus and interpeduncular fossa. This surgical route requires a pituitary transposition (or hypophysiopexy) to create a straight transsphenoidal trajectory toward the dorsum sellae. ¹ ^, ² It has been adopted by expert teams to manage selected cases of chordomas, craniopharyngiomas, or meningiomas invading the dorsum sellae, interpeduncular fossa, and/or third ventricle. ¹ ^– ⁵ Pioneering reports on the employment of transdorsal approaches to manage intracranial aneurysms have also been published. ⁶

Three types of hypophysiopexy with increasing difficulty and risk for postoperative hypopituitarism have been described. ¹ ^, ³ Extradural hypophysiopexy consists of a dislocation of the sellar content still protected by its periosteal envelope; this procedure (which is described in Chapter 11) represents an extension of the approach to the midclivus rather than a true transsellar transdorsal approach. ¹ ^, ³ The interdural hypophysiopexy takes advantage of the corridor between the pituitary gland and sellar tract of the internal carotid artery, requiring the sacrifice of the ipsilateral inferior hypophyseal artery. ² ^, ⁵ This anatomical route leads to the junction between the posterior wall of the cavernous sinus and the oculomotor triangle (i.e., the posterior half of the roof of the cavernous sinus) and can be exploited to reach the medial portion of the sylvian fissure. ⁷ ^– ⁹ Theoretically, this corridor can be harvested preserving the medial wall of the cavernous sinus, along either its medial (transsellar) or lateral (transcavernous) side. However, the medial wall of the cavernous sinus is frequently dehiscent and exceedingly delicate, thus being prone to laceration. Consequently, the variant of this approach, including the removal of the medial wall of the cavernous sinus, is described in the present chapter. Intradural hypophysiopexy consists of sectioning the diaphragma sellae on the midline, together with both inferior hypophyseal arteries, and transposing the pituitary gland in a cranial direction. This approach provides the widest upper transclival exposure among transnasal routes. ¹⁰ A partial transplanum–transtuberculum approach can be useful to control the most cranial portion of the surgical field. It is worth mentioning that most of the vascular supply of the pituitary gland comes from the inferior hypophyseal arteries. As a consequence, intradural hypophysiopexy is a procedure with a high risk for postoperative hypopituitarism.

Regardless of the specific type of hypophysiopexy, transdorsal approaches provide exposure of the interpeduncular fossa and related meningeal, vascular, and neural structures, creating the route between parasellar carotid arteries bilaterally, sellar floor inferiorly, and transposed pituitary gland superiorly (or medially for the interdural hypophysiopexy).

**Fig. 10.1 Sagittal view of the route toward the dorsum sellae and interpeduncular area.** This sagittal cadaver cut shows the trajectory from the nasal cavity to the sellar region and dorsum sellae. III, oculomotor nerve; AHyp, adenohypophysis; BA, basilar artery; CPr, carotid prominence; DoS, dorsum sellae; LOCR, lateral optic carotid recess; ON, optic nerve; OT, optic tract; P1, precommunicating tract of the posterior cerebral artery

**Fig. 10.2 Axial view of the dorsum sellae and adjacent structures.** This axial cadaver cut shows the dorsum sellae and neighboring structures. III, oculomotor nerve; AHyp, adenohypophysis; BA, basilar artery; CPe, cerebral peduncle; CS, cavernous sinus; DoP, periosteum of the dorsum sellae; LiM, Liliequist’s membrane; NHyp, neurohypophysis; P2, postcommunicating tract of the posterior cerebral artery; pcICA, paraclinoid tract of the internal carotid artery; PCoA, posterior communicating artery; PCP, posterior clinoid process; PWCS, posterior wall of the cavernous sinus; SCA, superior cerebellar artery; sICA, parasellar tract of the internal carotid artery; SpS, sphenoid sinus

After transgressing the dural layer, the arachnoid system of the posterior cranial fossa comes into view. The architecture and nomenclature of arachnoid membranes in this region are exceedingly complex and not universally accepted. Briefly, three groups of arachnoid membranes can be identified around the brainstem and cerebellum: (1) the tentorial group (which includes the posterior cerebral, lateral mesencephalic, superior cerebellar, and trigeminal membranes) is located adjacently to the tentorium and nearby the lateral surfaces of the mesencephalon and upper pons; (2) the clival group (which includes the Liliequist and anterior pontine membranes) lies between the clivus and the ventral surface of the mesencephalon and pons; (3) the perimedullary group (which includes the rhomboid membrane and denticulate ligaments) is formed by the arachnoid membranes surrounding the medulla oblongata and upper spinal cord. ¹¹ The key arachnoid structure in this area is the Liliequist membrane, which compartmentalizes the cisterns in front of the brainstem and surrounds cranial nerves and vessels of this area. In the anatomy laboratory, meticulous removal of arachnoid is of paramount importance to completely expose the neurovascular structures of the cisterns.

As an additional anatomical exercise, the reader is suggested to perform an inferior third ventriculostomy to analyze one of the possible pathways followed by chordomas and craniopharyngiomas to reach the third ventricle.

**Fig. 10.3 Sagittal and parasagittal MRI anatomy of the lamina terminalis, optic, interpeduncular, and prepontine cisterns. (a)** The upper left axial image summarizes the position of the following five sagittal (*white dotted lines*) and parasagittal (*white dashed line*) constructive interference in steady state (CISS) MRI **(b–f)**. The lamina terminalis cistern lies in front of the lamina terminalis (LT) and above the optic tract (OT) and chiasm (OCh). The optic cistern is enclosed between the optic chiasm and nerve (ON) superiorly and Liliequist’s membrane (LiM) posteroinferiorly. The interpeduncular cistern is delimited by the cerebral pedicles (CPe) bilaterally and Liliequist’s membrane anteriorly. Finally, the prepontine cistern is bounded by the anterior pontine membrane (APMe) anteriorly and pons (Po) posteriorly. The third ventricle (ThV) lies cranial to the interpeduncular cistern and shows an optic (ORe) and infundibular recess (InRe) toward the optic nerve and pituitary stalk, respectively. The oculomotor nerve (III) arises in the interpeduncular cistern and runs toward the cavernous sinus passing between the posterior cerebral artery and superior cerebellar artery (SCA), which can be double as in the present case. The posterior communicating artery (PCoA) runs parallel to the oculomotor nerve and above the posterior clinoid process (PCP), connecting the intracranial tract of the internal carotid artery (iICA) with the posterior cerebral artery. V, trigeminal stem; VI, abducens nerve; ACA, anterior communicating artery; AICA, anterior inferior cerebellar artery; BA, basilar artery; DoS, dorsum sellae; Hyp, hypophysis (pituitary gland); LaV, lateral ventricle; MBo, mammillary bodies; MeC, Meckel’s cave; P1, precommunicating tract of the posterior cerebral artery; P2, postcommunicating tract of the posterior cerebral artery; peICA, petrous tract of the internal carotid artery; SuPA, superior portion of the petrous apex; Ten, tentorium.

**Fig. 10.4 Axial MRI anatomy of the interpeduncular and prepontine cisterns.** The panel includes three axial constructive interference in steady state (CISS) MRI, from cranial **(a)** to caudal (lower image) **(c)**. The *white dotted lines* represent the position of the coronal images making up ▶Fig. 10.5. The posterior communicating artery (PCoA) arises from the posterior cerebral artery and reaches the intracranial tract of the internal carotid artery passing above the posterior clinoid process (PCP). This artery can maintain a remarkable caliber as a result of noninvolution of the fetal internal carotid artery. In particular, it is defined as “fetal posterior communicating artery” when it is larger than the precommunicating tract of the posterior cerebral artery. The oculomotor nerve (III) runs in the interpeduncular cistern, immediately below the posterior communicating artery, whereas the trigeminal stem (V) is located at the lateral boundary of the prepontine cistern. ACP, anterior clinoid process; BA, basilar artery; CPe, cerebral pedicle; DoS, dorsum sellae; GG, gasserian ganglion; MC, midclivus; P2, postcommunicating tract of the posterior cerebral artery; pICA, paraclival tract of the internal carotid artery; Po, pons; PSt, pituitary stalk; Ten, tentorium.

**Fig. 10.5 (a–f) Coronal MRI anatomy of the interpeduncular and prepontine cisterns.** The panel contains six coronal constructive interference in steady state (CISS) MRI passing through the interpeduncular and prepontine cisterns, from anterior **(a)** (upper left image) to posterior (lower right image) **(f)**. Liliequist’s membrane (LiM) inserts anteriorly on the dorsum sellae and posterior clinoid processes (PCP) and reaches laterally the oculomotor nerve (III). This nerve enters the posterior half of the roof of the cavernous sinus and is surrounded by a narrow cistern. The anterior choroidal artery (AChA) and posterior communicating artery (PCoA) arise from the intracranial tract of the internal carotid artery (iICA) and run above the oculomotor nerve. IV, trochlear nerve; V, trigeminal stem; V1, ophthalmic nerve; VI, abducens nerve; A1, precommunicating tract of the anterior cerebral artery; ACP, anterior clinoid process; BA, basilar artery; ChP, choroidal plexus; CPe, cerebral peduncle; Hyp, hypophysis (pituitary gland); MBo, mammillary bodies; MCA, middle cerebral artery; OCh, optic chiasm; ON, optic nerve; ORe, optic recess; OT, optic tract; Po, pons; P1, precommunicating tract of the posterior cerebral artery; pICA, paraclival tract of the internal carotid artery; PSt, pituitary stalk; SCA, superior cerebellar artery; sICA, parasellar tract of the internal carotid artery; Ten, tentorium; ThV, third ventricle; TuC, tuber cinereum.

Endoscopic Dissection

Nasal Phase

Paraseptal sphenoidotomy.
Transrostral sphenoidotomy.
Expanded transrostral sphenoidotomy.
Facultative: anterior ethmoidectomy.
Facultative: posterior ethmoidectomy.
Facultative: transethmoidal sphenoidotomy.

Skull Base Phase Intradural Hypophysiopexy

Transsellar approach.
Transplanum–transtuberculum approach.
Step 1: Opening of the optic cistern, incision, and removal of the diaphragma sellae.
Step 2: Opening of the lamina terminalis cisterns.
Step 3: Infrahypophyseal dissection and sectioning of the inferior hypophyseal artery.
Step 4: Intradural hypophysiopexy.
Step 5: Removal of the posterior sellar periosteum.
Step 6: Removal of the dorsum sellae and posterior clinoid processes.
Step 7: Incision of the dorsal periosteum and dura mater.
Step 8: Incision of the anterior pontine membrane.
Step 9: Incision of the sellar and mesencephalic portions of the Liliequist membrane.
Step 10: Removal of the diencephalic portion of the Liliequist membrane and other arachnoid membranes.
Step 11: Ventriculostomy between the mammillary bodies and tuber cinereum.