Microanatomy of endoscope-assisted glabellar nasal keyhole approach.

OBJECTIVE: To make a study of the detailed microanatomy of endoscope-assisted glabellar nasal keyhole approach (GNKA) to be used clinically. METHODS: 10 dry adult Chinese skulls were measured and 10 perfused cadaveric heads were dissected to mimic the GNKA. RESULTS: Average distances between bilateral supraorbital foramen/incisure, supratrochlear incisure, medial orbital wall were 47.71+/-3.61 mm, 33.67+/-3.82 mm and 24.34+/-1.29 mm, respectively, in dry skulls. Average distance from nasion to medial inter-canthus line (ICL) was 10.31+/-1.02 mm in cadaveric heads. The nasion was 3.95+/-0.45 mm above the cribriform plate (CP) and the ICL is 6.25+/-0.71 mm below. With the assistance of endoscopes, GNKA can expose all extradural structures near the midline from the anterior skull base to the ventral brain stem corresponding to the clivus. The exposed clival dura was 19.18+/-1.44 mm in width and 25.44+/-1.25 mm in length. Intradural structures such as frontal base, parasellar area, longitudinal fissure and the third ventricle floor, can also be exposed. CONCLUSION: GNKA is a minimally invasive and effective anterior skull base approach. Determining the inferior margin of incision by ICL instead of nasion is more convenient and can expose the subcranial area better.