Do Benign Mass Lesions in the Superficial Lobe of Parotid Gland Influence Landmark-Based Search for Facial Nerve Trunk at Surgery?

Objective: To assess the influence of benign mass lesions in the superficial lobe of parotid on the known anatomic landmarks for identifying the facial nerve trunk.
Method: Patients with unilateral biopsy-proven benign mass lesions in the superficial parotid were selected for this observational study. During superficial/partial superficial parotidectomy, distance of the facial nerve trunk from each landmark was assessed using spring calliper and correlated with the lesion’s volume (measured from the pre-operative imaging). At least two identifiers among tragal pointer (TP), posterior belly of digastric muscle (PBDM) and tympanomastoid suture (TMS) were considered.
Results: The study involved 32 patients. The lesions mostly involved the parotid tail (50%) and pretragal region (34.3%), and constituted of pleomorphic adenoma (~66%) and Warthin’s tumor (~9%), the rest being various cysts and hamartomas. TP was universally uncovered, while PBDM and TMS were exposed in 26 and 25 patients, respectively. Average distances between the facial nerve trunk and TP, PBDM and TMS were 12.79 mm (SD=2.33), 9.78 mm (SD=1.21) and 7.58 mm (SD=1.33), respectively. Correlation coefficients between the lesion’s volume and the distance of facial nerve from a given landmark were -0.11, 0.04 and -0.16 for TP, PBDM and TMS, respectively.
Conclusions: TP was the most easily available landmark on surgical dissection, while PBDM was the most consistent and the least variable when volumetric data of the benign mass lesions in the superficial lobe of parotid were considered as a factor influencing the distance from the facial nerve trunk.