Displacement of the Facial Nerve by Deep Parotid Lobe Lesions in the Pediatric Population

Incidence of Displacement of Facial Nerve Trunk from Normal Anatomical Position in Cases of Benign Tumour in Superficial Lobe of Parotid Gland: A Surgical Finding and its Significance

Purpose of current study was to find out the incidence of displacement of facial nerve trunk from its normal anatomical position in relation to size and site of tumour in superficial lobe of parotid gland and its surgical significance. In the literature, the importance was given to the anatomical variations in branching pattern of facial nerve but not deviation. The knowledge of this variation is very important to prevent its injuries during superficial parotidectomy. The present study included 60 patients who underwent superficial parotidectomy for benign tumour involving the superficial lobe of parotid gland. The site and size of tumour noted pre operatively with help of ultrasound and CT scan and pathological diagnosis was made by FNAC. The superficial parotidectomy was performed and facial nerve was identified in all cases. In our study, 23 patients out of 60 were having displacement of facial nerve trunk from its normal anatomical position found during superficial parotidectomy. 10 out of 13 patients with tumor superior to facial nerve trunk were having displacement, 7 out of 18 had deviation with tumor inferior to nerve, 6 out of 29 patients had deviation of main trunk when the tumor involved whole of superficial lobe of gland.We conclude that the facial nerve trunk cannot be always traced at normal anatomical position by following the documented anatomical landmarks because of its displacement by tumour. Knowledge of this variation of facial nerve trunk can avoid the chances of damage to this nerve during superficial parotidectomy.

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.

Conclusion

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.