21 The Suprapetrous (Meckel’s Cave) Approach

10.1055/b-0039-172583

21 The Suprapetrous (Meckel’s Cave) Approach

Vittorio Rampinelli, Marco Ravanelli, Marco Ferrari, Davide Lancini, Alberto Schreiber

Meckel’s cave is a cisternal space bounded by the dura and the periosteum that is located in the inferolateral portion of the parasellar area, which corresponds to the medial portion of the middle cranial fossa. It neighbors the cavernous and sphenoid sinuses medially, temporal lobe of the brain superolaterally, middle cranial fossa inferolaterally, and petrous tract of the internal carotid artery inferiorly. Meckel’s cave houses several neural fibers running within the cerebrospinal fluid and merging to form the gasserian ganglion, which is also called the semilunar ganglion due to its crescent shape. The ophthalmic, maxillary, and mandibular nerves arise from the gasserian ganglion and run toward the superior orbital fissure, foramen rotundum, and foramen ovale, respectively.

As a natural consequence of its preeminent content in neural structures, Meckel’s cave and adjacent areas mostly harbor neurogenic lesions, especially schwannomas and malignant peripheral nerve sheath tumors, the latter being exceedingly rare. ¹ ^– ¹⁰ Secondarily, this area can be involved by several diseases that are located at the borderline between the lateral portion of the cavernous sinus and Meckel’s cave, including sinonasal/nasopharyngeal malignancies (especially when exhibiting perineural spread like adenoid cystic carcinomas, squamous cell carcinomas, or nasopharyngeal carcinomas), ¹ ^, ⁸ ^, ⁹ ^, ¹¹ bone–cartilage-arising tumors (i.e., chordomas, chondrosarcomas), ¹ ^, ² ^, ⁵ ^, ⁹ ^, ¹² meningiomas, ¹ ^, ⁵ ^, ⁹ pituitary adenomas, ¹ ^, ² juvenile angiofibromas, ¹ ^, ² ^, ¹¹ epidermoid, neuroenteric, or endodermal cysts, ¹ ^, ² ^, ⁵ ^, ¹³ metastases, ⁸ ^– ¹⁰ ^, ¹³ lymphomas, ⁸ ^, ⁹ neurosarcoidosis, ⁸ ^, ⁹ and other rare lesions. ¹ ^, ⁹ ^, ¹⁴ ^, ¹⁵ The endoscopic transnasal approach has been adopted by some pioneering groups to remove or obtain a biopsy of these diseases. ¹ , ³ ^– ⁸ ^, ¹⁰ ^– ¹² ^, ¹⁴ ^– ¹⁶ More recently, the endoscopic transorbital corridor was also adopted as the sole or ancillary approach to manage some lesions involving the parasellar area and the middle cranial fossa. ¹⁷ ^, ¹⁸

**Fig. 21.1 Intracranial superolateral-to-inferomedial view of the parasellar area.** This cadaver picture shows with a superolateral-to-inferomedial intracranial perspective the right parasellar area. III, oculomotor nerve; IV, trochlear nerve; V, trigeminal stem; V1, ophthalmic nerve; V2, maxillary nerve; V3, mandibular nerve; VI, abducens nerve; ACP, anterior clinoid process; CS, cavernous sinus; DSe, diaphragma sellae; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; iICA, intracranial tract of the internal carotid artery; LSPN, lesser superficial petrosal nerve; ON, optic nerve; PLLi, petrolingual ligament; sICA, parasellar tract of the internal carotid artery; SPS, superior petrosal sinus.

**Fig. 21.2 Axial view of the Meckel’s cave and adjacent areas.** This axial cadaver cut shows with an inferior-to-superior perspective the left Meckel’s cave. The cut has been performed through the trigeminal stem (V), trigeminal fibers within the Meckel’s cave (Vf), gasserian ganglion (GG), maxillary nerve (V2), and infraorbital nerve (ION). CS, cavernous sinus; ITF, infratemporal fossa; OrF, orbital floor; pICA, paraclival tract of the internal carotid artery; Po, pons; PPF, pterygopalatine fossa; SER, sphenoethmoidal recess; SpS, sphenoid sinus; TL, temporal lobe of the brain.

This chapter includes three modular extensions of the endoscopic transnasal approach to Meckel’s cave: (1) the classic suprapetrous approach, formerly called the “front door to Meckel’s cave,” takes advantage of the quadrangular space defined by the petrous and paraclival tracts of the internal carotid artery caudally and medially, abducens nerve cranially, and maxillary nerve laterally ¹ ^, ¹⁶ ^, ¹⁹ ; (2) the extension through the superior transpterygoid approach takes advantage of the space gained by sectioning the inferior orbital fissure and allows exposure of the entirety of the mandibular nerve, from the gasserian ganglion to the infratemporal fossa ²⁰ ^, ²¹ ; and (3) the “transalisphenoid” approach includes partial removal of the greater sphenoidal wing, thereby providing wide access to the middle cranial fossa through the spaces between the trigeminal branches. ¹¹

**Fig. 21.3 Axial MRI anatomy of the trigeminal system.** This axial CISS (constructive interference in steady state) MRI passes through the trigeminal stem (V), Meckel’s cave (MeC), and superior orbital fissure (SOF). Meckel’s cave lies between the cavernous sinus (CS) medially and the temporal lobe of the brain laterally. It is a cisternal space where the trigeminal fibers (Vf) run free within the cerebrospinal fluid before forming the gasserian ganglion (GG). These structures are aligned with the superior orbital fissure (SOF). *White lines* (A–G) show the position of images composing ▶Fig. 21.4. BA, basilar artery; BaP, basilar plexus; MC, midclivus; Po, pons; SpS, sphenoid sinus.

**Fig. 21.4 (a–g) Coronal MRI anatomy of the trigeminal system and adjacent structures.** The panel includes seven coronal CISS (constructive interference in steady state) MRI images passing through different portions of the trigeminal system, from posterior **(a)** to anterior **(g)**. The trigeminal stem (V) runs close to the superior cerebellar artery (SCA) in the prepontine cistern. Then, it enters Meckel’s cave (MeC) passing through the trigeminal porus (TPo), which is a dural passage located between the superior (SPS) and inferior petrosal sinuses (IPS). Within Meckel’s cave, the trigeminal stem splits into several fibers (Vf) that run free within the cerebrospinal fluid and merge anteriorly to form the gasserian ganglion. Finally, the gasserian ganglion gives the three branches of the trigeminal nerve, namely, the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic nerve runs within the lateral wall of the cavernous sinus reaching the superior orbital fissure (SOF) together with the oculomotor (III), trochlear (IV), and abducens nerve (VI). The maxillary nerve runs within the base of the pterygoid process (BP) passing through the foramen rotundum. The mandibular nerve passes through the foramen ovale, where it is surrounded by the foraminal venous plexus (FoPl), and reaches the infratemporal fossa. AIPA, anteroinferior petrous apex; BA, basilar artery; cET, cartilaginous portion of the eustachian tube; Co, cochlea; DoS, dorsum sellae; FCB, fibrocartilago basalis; GW, greater wing of the sphenoid bone; h, horizontal portion of the petrous tract of the internal carotid artery; Hyp, hypophysis; IMA, internal maxillary artery; LiP, lingual process; LoC, lower clivus; LoLP, lower head of the lateral pterygoid muscle; MC, midclivus; MMA, middle meningeal artery; MPM, medial pterygoid muscle; NaV, nasopharyngeal vault; peICA, petrous tract of the internal carotid artery; pICA, paraclival tract of the internal carotid artery; PLLi, petrolingual ligament; Po, pons; PtPl, pterygoid plexus; sICA, parasellar tract of the internal carotid artery; SpF, sphenoidal floor; SpS, sphenoid sinus; SuPA, superior petrous apex; UpLP, upper head of the lateral pterygoid muscle; v, vertical portion of the petrous tract of the internal carotid artery; VC, vidian canal.

**Fig. 21.5 Axial and parasagittal MRI anatomy of the trigeminal system and adjacent structures.** The panel includes one axial **(a)** and two parasagittal **(b, c)** CISS (constructive interference in steady state) MRI images passing through the trigeminal system and adjacent structures. The *white dashed lines* (A and B) depict the orientation of the parasagittal images. The petrolingual ligament (PLLi) goes from the superior portion of the petrous apex (SuPA) to the lingual process of the sphenoid bone, passing above the petrous tract of the internal carotid artery (peICA), lateral to the paraclival tract of the internal carotid artery, and medial to Meckel’s cave (MeC). This ligament is particularly important as it is intimately related to several important neurovascular structures, namely, the abducens nerve (VI), the gasserian ganglion (GG), the maxillary nerve (V2), and the mandibular nerve (V3). The gasserian ganglion is formed by several fibers (Vf) arising from the trigeminal stem (V). This ganglion is also called semilunar due to its crescent shape (*white dotted line*). The ophthalmic nerve (V1) runs from the gasserian ganglion to the superior orbital fissure, which is separated from the foramen rotundum (FRo) by the maxillary strut (MSt), a bony structure connecting the body of the sphenoid with the greater wing of the sphenoid. Similarly, the mandibular strut (MaSt) is a bony bridge connecting the base of the pterygoid process (BP) with the greater wing of the sphenoid and separating the foramen rotundum from the foramen ovale (FOv). The Vesalius foramen (VeF) is an inconstant bony canal, which contains a vein and passes through the mandibular strut. AFB, acoustic-facial bundle; BA, basilar artery; BaP, basilar plexus; MC, midclivus; Po, pons; SpS, sphenoid sinus; VC, vidian canal.

Endoscopic Dissection

Nasal Phase

Paraseptal sphenoidotomy.
Transrostral sphenoidotomy.
Expanded transrostral sphenoidotomy.
Total uncinectomy.
Anterior ethmoidectomy.
Posterior ethmoidectomy.
Type A endoscopic medial maxillectomy.
Facultative: optic and orbital decompression.
Facultative: type B–D endoscopic medial maxillectomy.

Skull Base Phase Suprapetrous Approach

Facultative: Transsellar approach.
Facultative: Transclival (midclivus) approach.
Facultative: Transcavernous (lateral) approach.
Step 1: Removal of the carotid prominence, lateral wall of the sphenoid sinus, and maxillary strut.
Step 2: Partial exposure of the vidian canal and the foramen rotundum.
Step 3: Incision of the quadrangular space.
Step 4: Exposure of the petrous apex.