The slope in the midline of the skull base consists of the anterior wall of the posterior cranial fossa, with a total length of 45.0 mm. anterior to the slope are the parietal pharynx, nasopharynx and posterior wall of the oropharynx; posterior to the slope are the dura mater, the ventral side of the brainstem and the vertebrobasilar artery. Intradural tumors in the slope area include meningioma, nerve sheath tumor and cholesteatoma, etc.; epidural tumors include chordoma, osteochondroma, chondrosarcoma, chondrosarcoma and other osteogenic tumors, and it is very difficult to cure slope tumors.
There are many surgical approaches in the slope area. The choice of the approach should be based on the anatomical relationship between the lesion site and the slope and dura, and the surgical approach that can maximize the resection of the tumor, protect the surrounding important tissues and minimize the secondary damage should be chosen. At present, there are mainly anterior approach and lateral approach in slope area.
1. Anterior approach
1.1 Anterior skull base approach
Tessier used the anterior cranial base approach to deal with craniofacial deformities, which was later modified by Derome for the resection of epidural midline tumors in the middle and posterior cranial fossa.
1.2 Extended transsphenoidal sinus approach
Laws first proposed the transsphenoidal sinus approach for resection of slope tumors, while the extended transsphenoidal sinus approach is mainly used for midline epidural lesions and is suitable for resection of mid and upper slope tumors.
1.3 Midface Revision Approach
Casson used a nasal molding and nasal vestibular incision, combined with subperiosteal separation of the maxilla, to establish the concept of the midface reversal approach. This approach allows for good exposure of the septal sinus, pterygoid sinus, nasopharynx, and slope without leaving an incision in the face.
1.4 Transoral approach
The Crockard transoral approach has been successful in removing intradural lesions in the atlanto-occipital region. This approach is particularly useful in removing tumors ventral to the superior and inferior occipital foramen and in managing bony malformations ventral to the brainstem.
1.5 Facial lift approach
The standard facial lift approach and the expanded facial lift approach advocated by Janecka provide adequate exposure of the nasopharyngeal and slope areas. Because the inferior temporal fossa is integrated with the entire operative field, it allows for reversal of the hemorrhagic temporalis flap for reconstruction of the skull base defect.
2. Lateral approach
2.1 Posterior suboccipital sigmoid sinus approach
The posterior suboccipital sigmoid sinus approach for resection of tumors in the slope area is similar to the approach used for resection of auditory neuromas. samii describes a modified posterior sigmoid sinus approach-i.e., the posterior sigmoid sinus intradural superior approach to the internal auditory tract, which involves a posterior suboccipital sigmoid sinus craniotomy, abrasion of the superior internal auditory tract, and access to the middle cranial fossa.
2.2 Suboccipital extreme lateral approach
Since the 1970s, Spetzler has used the lateral inferior occipital pole approach to manage lesions on the inferior slope, foramen magnum, and ventral aspect of the superior cervical segment. Good results can be achieved as long as the operator has good skull base surgical skills and works with an otologic specialist.
2.3 Transosseous-cerebellar curtain approach
Hakuba modified the transcranial-cerebellar curtain approach to form a rock-bone-cerebellar curtain approach to remove the slope – apical tumor, i.e., partial resection of the temporal bone is performed before the supratentorial and subcranial reveal of the tumor.
2.4 Apical-cerebellar approach
Most slope meningiomas originate in the chondrogenic region of the pterygo-occipital region and grow into the middle and posterior fossa of the skull. Because of the brittle and soft bone in the apical region, even small to medium-sized slope meningiomas often involve the apices, forming pterygo-rock slope meningiomas. For such lesions, Kawase proposed an apical-cerebellar approach.
2.5 Inferior temporal-anterior inferior temporal fossa approach
Sekhar designed the infratemporal-anterior infratemporal fossa approach to resect tumors involving the rock-oblique region, pterygoid region, cavernous sinus, middle cranial fossa, infratemporal fossa, posterior pharynx, and parapharyngeal region. Since then, the orbitozygomatic-inferior temporal fossa approach has been improved by Al-Mefty and has become one of the most widely adapted skull base approaches.
In recent years, Prof. Fred Gentili from Toronto, Canada and China-International Neuroscience Institute advocated endoscopic techniques for slope tumors, while Prof. Wolfgang Draf, Madjid Samii from Hannover, further combined endoscopic techniques with microsurgical techniques for slope tumors, achieving more satisfactory results.