Microsurgical anatomic features of the olfactory nerve: relevance to olfaction preservation in the pterional approach.
OBJECTIVE: The pterional approach represents the standard approach for most lesions of the anterior and middle cranial fossa. It requires some degree of frontal lobe retraction, which may result in temporary or permanent damage of olfaction because of nerve avulsion or mechanical compression. The purpose of this study, based on microanatomic dissection of human cadaveric specimens, was to review the microsurgical anatomic features of the nerve and suggest operative nuances that may contribute to reducing the rate of postoperative olfactory dysfunction. METHODS: Twenty olfactory nerves and tracts were examined in 10 human cadaveric heads obtained from three fresh and seven formalin-fixed adult cadavers. A standard pterional craniotomy was performed. The olfactory nerve was dissected from its arachnoidal envelopes and then mobilized for an average length of 30 mm (range, 25-35 mm). RESULTS: The possible retraction of the frontal lobe was 10 to 15 mm. More retraction invariably resulted in nerve disruption. CONCLUSION: The standard sylvian and basal cistern opening may be insufficient to guarantee preservation of olfactory function. Early identification and arachnoidal dissection of the nerve may reduce the rate of olfaction compromise. The opening of the subarachnoidal space should be performed in a proximal-to-distal manner to allow early visualization of the olfactory bulb and its dissection. The arachnoidal dissection should be performed with sharp instruments, avoiding any traction on the posterior portion of the olfactory tract. Any direct retractor compression should also be avoided to spare the microvasculature lying on the dorsal surface of the nerve.