Use of the medial canthal point (MCP) as a reliable anatomical landmark to the frontal sinus

Frontal sinus surgery is considered one of the more challenging aspects of Functional Endoscopic Sinus Surgery, due to the complex variations in normal sinus anatomy but also increased morbidity due to the close proximity of critical structures such as the anterior cranial fossa and orbits. We aim to investigate the medial canthal point (MCP) as an anatomical landmark for safe frontal sinus access.

The MCP intranasally is identified during surgery with non-tooth forceps, with one limb just anterior to the medial canthus and the other intranasally in the same coronal plane along the skull base. This point was identified on 100 paranasal sinus computed tomography (CT) scan reconstructions. The distance between the anterior cranial fossa and MCP was measured on imaging-medial canthal point distance (MCPD). The maximal anterior-posterior (AP) distance was measured on all scans.

The average MCPD for males was 13.0 mm (8.7-20.4 mm) and for females 12.0 mm (6.8-22.8 mm). Mean AP distance for males was 12.0 mm (4.5-20.2 mm) and for females 10.4 mm (3.8-15.9 mm). Mean distance for all 100 patients was 12.6 mm (range 7.5-22.8 mm). In all cases, the MCP was anterior to the cranial fossa. Mixed effects modelling analysis showed a significant correlation between the MCPD and AP distance (P = .006).

The MCP is a consistent anatomical landmark that can serve as an adjunct to safe frontal sinus access alongside the first olfactory fiber and CT navigation systems. However, patient selection continues to be very important, with larger well pneumatized frontal sinuses being ideal to tackle earlier in a surgeon's career.

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