Surgical anatomy and variations of the infraorbital nerve.

OBJECTIVES/HYPOTHESIS To assess relevant variations in the anatomical course of the infraorbital nerve (ION). This understanding may reduce the risk of surgical injury. METHODS A total of 100 consecutive computed-tomography sinus studies obtained in a tertiary referral center were reviewed, and measurements were made of the 200 IONs. Anatomic variants were classified into three types based on the degree to which (if any) the nerve's course descended from the maxillary roof into the sinus lumen. RESULTS A total of 60.5% of IONs were entirely contained within the sinus roof. In 27.0%, the nerve canal descended below the roof but remained juxtaposed to it. In 12.5%, the ION descended into the sinus lumen. The proportion of IONs descending into the sinus significantly increased to 27.7% when an infraorbital ethmoid cell was present (chi-square P < 0.001) and to 50% when the nerve was contained within a lamella of such a cell (chi-square P < 0.001). Descended nerves terminated in a foramen located an average of 11.9 ± 2.5 mm below the infraorbital rim, significantly further below the orbit than nondescended nerves (t test P < 0.001). Descended nerves were located a mean distance of 8.6 ± 2.9 mm below the sinus roof and traversed the sinus lumen diagonally for a mean length of 15.4 ± 3.1 mm. CONCLUSIONS Descent of the ION into the maxillary sinus is a common anatomic variant that is more prevalent in the setting of an ipsilateral infraorbital ethmoid cell. Descended nerves are associated with the foramen significantly further below the inferior orbital rim than those of nondescended nerves. These observations may help surgeons avoid iatrogenic ION injury. LEVEL OF EVIDENCE N/A.