2 Nasal Corridors
Endoscopic surgery of the skull base and adjacent areas takes advantage of the natural corridor of the sinonasal tract. This concept represents an extension of functional endoscopic sinus surgery, in which natural drainage pathways are followed to open the sinuses. 1 – 4 Even though employed as corridors toward the skull base, sinonasal cavities should be dissected following the principles of functional surgery as much as possible, aiming at avoiding unnecessary morbidity and minimizing postoperative complications. The first step when starting the surgical procedure is to examine the natural corridors of the nasal cavity in order to get oriented. The lumen of the nasal cavity is irregularly shaped: on the medial side, it takes the shape of the nasal septum and can be accordingly narrowed or enlarged by its deviations and spurs; the lateral side consists of the turbinates and related nasal meati, which can be enlarged by pneumatization (i.e., concha bullosa) or present an everted shape (i.e., paradoxical turbinate); the caudal surface corresponds to the nasal floor and is usually flat and regular; the cranial boundary of the lumen is the olfactory cleft (or fissure), which is a narrow niche enclosed between the highest portions of middle and superior turbinates laterally and nasal septum medially.
Endoscopic skull base surgery is based on the profound knowledge of anatomical landmarks, which provide the surgeon with a mental scheme to depict where neurovascular and musculoskeletal structures are located before exposing them. 4 – 14 As a consequence, understanding of anatomy in an untouched nasal cavity is indispensable and of paramount importance to plan and proceed with safe and oriented surgery. With the intent to facilitate the identification of sinonasal landmarks, the nasal cavity has been divided into three nasal corridors, as follows:
Inferior nasal corridor: Between the inferior turbinate and nasal septum.
Middle nasal corridor: Between the bulbous portions of middle and superior turbinates and nasal septum.
Superior nasal corridor: Between the common laminar portion of middle and superior turbinates and nasal septum.
The inferior nasal corridor runs from the nasal vestibule to the nasopharynx along the nasal floor. It can be merged with the contralateral one by removing the nasal septum; usually, a posteroinferior septectomy is sufficient when addressing the craniocervical junction and neighboring areas. Laterally, the corridor can be expanded passing through the palatine bone, pterygoid process, and maxillary sinus to access the upper parapharyngeal space, pterygopalatine fossa, and infratemporal fossa.
The middle nasal corridor provides a straight trajectory toward the sphenoid sinus. It can be merged with the contralateral corridor with a posterosuperior septectomy. On the lateral side, the corridor can be expanded through the ethmoid complex, medial orbital wall, and lateral sphenoidal wall to reach the orbital cavity, Meckel’s cave, and cavernous sinus.
The superior nasal corridor guides toward the midline anterior skull base and can be fused with the contralateral one with removal of the entire nasal septum. This corridor is oriented toward the olfactory grooves and can be extended laterally through the ethmoidal compartments to expose the ethmoidal roof (also called fovea ethmoidalis).
Step 1: Exploration of the inferior nasal corridor.
Step 2: Lateralization of the inferior turbinate.
Step 3: Exploration of the inferior nasal meatus.
Step 4: Exploration of the middle nasal corridor.
Step 5: Lateralization of the middle and superior turbinates.
Step 6: Exploration of the middle nasal meatus.
Step 7: Exposure of the sphenopalatine artery.
Step 8: Exploration of the superior nasal corridor