Table 1. Description of the four types of approaches.

	SLC	PC	PS	LCR
Target area	Orbital apex and roof, ACF, frontal sinus	ACF, lateral nasal cavity, CS, and ON	Inferior orbit	Lateral part of ACF; supraclinoid ICA, ON, temporal lobe, Sylvian fissure, petrous apex
Key landmarks	Superior orbicularis oculi muscle	Anterior and posterior ethmoid artery, ON, orbital roof	Inferior orbicularis oculi muscle; inferior orbital septum; orbital rim	Canthal lateral ligament; IOF, SFS, and SOF
Approach brief description	Incision at superior eyelid; dissection through orbicularis oculis muscle to obtain a skin-muscle flap turned toward the orbit, dissection is performed by scope in a preseptal plane	Incision starts at the junction of conjunctiva and skin, medial the caruncle, exposing the medial orbital wall in a top-bottom direction. Dissection follows the medial canthal tendon until the posterior lacrimal crest, where periosteum is incised allowing to lift superolaterally the periorbita up to the anterior ethmoid artery	Incision of the conjunctival surface of the lower eyelid, 2 mm below tarsus and 6 mm inferior to eyelid margin. Orbicularis oculi muscle is identified, and the dissection is performed; then periosteum is incised at the posterior aspect of the orbital rim, leaving the infraorbital nerve on the orbital floor	Incision starts posteriorly to canthal tendon that is retracted laterally. Periorbit is dissected medially allowing the endoscopic access; using a 30-degree scope, the SFS is identified; by drilling the bone area above and lateral, it is possible to access the lateral part of ACF, whereas by drilling the bone above and medial, it is possible to reach ICA and ON. By drilling bone area below to SFS, it is possible to access the MCF, Sylvian fissure, temporal lobe and cavernous sinus
Potential pathologies	ACF and frontal sinus lesions	Sellar, parasellar, CS, ON lesions	MCF, Meckel's cave, and lateral wall of cavernous sinus	Lateral ACF, middle fossa, Sylvian fissure and petrous apex regions lesions

Abbreviations: ACF, anterior cranial fossa; CS, cavernous sinus; ICA, internal carotid artery; IOF, inferior orbital fissure; LCR, lateral retrocanthal approaches; MCF, middle cranial fossa; ON, optic nerve; SFS, sphenofrontal suture; SOF, superior orbital fissure.