**1. Introduction**

This chapter shows the anatomically based bone removal to the original middle cranial fossa surgery method, which is difficult to reach using microscopy alone [1, 2]. The author advocates a safe method of reaching the middle cranial fossa surgery by rationally approaching the cavernous sinus, pterygopalatine fossa, paranasal sinuses from the cranial side, pharynx, and medial jugular foramen from the microanatomical viewpoint [3–5].

In addition, the anatomical relationship with the paranasal sinuses and Eustachian tubes will further enhance the anatomical understanding of transnasal endoscopic surgery. Safe bone removal is paramount in skull base surgery. In this article, it is possible to approach the petrous bone, clivus, sphenoid sinus, maxillary sinus, and ethmoidal sinuses from the infratemporal fossa. Furthermore, understanding the layered structure of the cavernous sinuses will allow for a rational choice of approach to the surgical target and method of tumor removal [6–8].

The various approaches to skull base surgery have a history of significant development through collaboration with pyramidal bone surgery in otolaryngology. As a result, the deepest region, the skull base, can now be safely reached using the pyramidal bone route to the depths of the skull base. Furthermore, since around 2000, neuroendoscopes have been introduced, and transnasal endoscopic surgery has been advocated for the approach through the sphenoid sinus to the sella turcica tumor, the clivus, and the pyramidal bone area [2, 9–13]. In addition, the transcranial approach to reaching surgery has made it possible to use endoscopes to observe deeper regions, expanding the variation of surgery to areas that could not previously be observed with microsurgery. However, despite advances in surgical methods that allow access to the skull base without craniotomy, one of the advantages of nasal endoscopic surgery, it has gradually become clear that endoscopic surgery still has its disadvantages.

Although the surgical wound is not visible in transnasal endoscopic surgery, damage to the mucosa of the nasal cavity can be significant. Because the structures within the nasal cavity have been destroyed, the nasal environment may deteriorate, resulting in nasal contamination, olfactory disturbances, and other symptoms [14].

The most problematic complication is CSF leakage. As safe and reliable methods have been established, the most rational method is selected for each disease based on the direction of tumor extension, site of origin, and surrounding anatomy, craniotomy, endoscopic surgery, and combined approaches of open and endoscopic surgery can be performed safely in response to clinical variations [15–18].

In addition to the conventional middle cranial fossa craniotomy, we have further expanded the range of surgical approaches to the cavernous sinus around the trigeminal nerve by removing bone within a safe range, and by introducing an endoscope, we have expanded the scope of surgical approaches to the cavernous sinus, the inferior cranial nerve, the sinus cavity, and the pterygopalatine fossa. Furthermore, the nasal endoscope was used to approach the cavernous sinus from the pterygopalatine fossa (PPF), and the possibility of treatment from both sides was examined, and the advantages and disadvantages of this approach are discussed.

## **2. Anatomical structures**

#### **2.1 Inferior orbital fissure (IOF)**

The IOF is defined as a space between the lateral wall and floor of the orbit. The IOF runs in a direction from the maxillary strut posteriorly to the zygomatic bone anteriorly. The zygomatic nerve (ZyN) of the maxillary nerve, infraorbital nerve (ION), orbital ganglionic branch of PPG, infraorbital artery, and inferior division of ophthalmic vein pass through the IOF [19].

#### **2.2 Muller's muscle (MM)**

Muller's muscle, an embryological remnant of the retractor bulbi in mammals, can be identified over the IOF and it blends with the periosteum. Muller's muscle forms a bridge over the IOF, separating the orbital content from the PPF [19].

#### **2.3 Zygomatic nerve (ZyN)**

The zygomatic nerve (ZyN) is the first branch of the maxillary nerve that divides off after emerging from the FR to enter the PPF. The ZyN can be found

### *Surgical Approach to the Cavernous Sinus and Middle Cranial, Pterygoid Fossa DOI: http://dx.doi.org/10.5772/intechopen.104956*

about 5 mm distal from the anterior point of the maxillary strut. Coursing superiorly, it enters the orbit laterally through the IOF. It divides two branches distally, the zygomaticotemporal nerve, which is parasympathetic branch and connected lacrimal nerve, and the zygomaticofacial nerve, which is a sensory branch carried from the skin of the zygomatic area [20].
