Ringing the Bell’s: A Mohs complication worth listening to – A case report

Abstract

We report an uncommon case of transient Bell’s palsy-like facial paralysis following local anesthesia during Mohs micrographic surgery of the left conchal bowl. The temporary complication resolved spontaneously without intervention and is suspected to have resulted from anesthetic diffusion to the facial nerve via the tragal region. This case highlights the importance of understanding facial nerve anatomy during procedures in the auricular area and the need to counsel patients regarding rare but benign complications of local anesthesia.

Introduction

Mohs micrographic surgery (MMS) is the gold standard for treating high-risk nonmelanoma skin cancers in cosmetically and functionally sensitive areas such as the ear. Though generally safe, MMS can result in rare complications, including transient facial nerve paralysis due to inadvertent anesthetic diffusion. ¹ In this report, we describe a case of temporary Bell’s palsy-like symptoms following MMS of the left conchal bowl, likely related to the proximity of the injected anesthetic to facial nerve branches. To our knowledge, only a handful of reports exist describing facial palsy after local anesthesia in the auricular region, and even fewer in the specific context of MMS to the conchal bowl. This reinforces the need for anatomical awareness and enhanced informed consent in ear-centered Mohs procedures.

Case presentation

A 67-year-old woman presented with a 1.2 × 1.2 cm biopsy-proven basal cell carcinoma of the left conchal bowl. The lesion was excised via standard MMS protocol and technique under local infiltration with lidocaine hydrochloride and epinephrine 1:100,000 (6 cc). Three stages were required to achieve tumor-free margins.

Prior to stage two, additional 1% lidocaine with epinephrine was administered. The patient developed facial asymmetry with signs consistent with transient facial paralysis, including upper and lower facial weakness on the ipsilateral side. She had no prior history of Bell’s palsy nor neurologic conditions. The postoperative note documented the likely cause as a transient anesthetic effect on the facial nerve near the tragus. Symptoms had largely resolved by the time of discharge without any specific intervention (Figure 1).

Figure 1.

Transient facial nerve paralysis after Mohs surgery of the conchal bowl.

Discussion

Facial nerve palsy following MMS is an uncommon but clinically significant complication, particularly when procedures are performed in the periauricular region where branches of the facial nerve are more superficial. The temporal and zygomatic branches, in particular, are susceptible to anesthetic spread or iatrogenic trauma during surgery involving the auricle, conchal bowl, or tragus. ²

Majerowski et al. described three cases of transient facial nerve palsy during dermatologic surgery involving the preauricular cheek and mandibular angle. In each instance, paralysis was temporary and resolved without residual deficits, reinforcing that conservative management is often sufficient and that invasive workup is rarely necessary in the absence of other concerning features. ³ Similarly, Vasandani et al. reported a case of facial paralysis immediately following lidocaine with epinephrine injection for a pinna laceration repair. The patient experienced complete symptom resolution within 4 hours. ⁴ These cases highlight the proximity of facial nerve branches to injection sites in the external ear and adjacent tissues.

In the otolaryngologic literature, facial palsy has been described after local anesthesia administered near the mastoid tip or external auditory canal, with symptoms attributed to diffusion toward the stylomastoid foramen. ⁵ This mechanism is consistent with known anatomic pathways: the facial nerve exits the stylomastoid foramen and travels anteriorly within the parotid gland before branching across the face. Even small volumes of anesthetic can theoretically diffuse through fascial planes and transiently impair nerve conduction.

Parallel complications have been described in dental practice, where transient facial paralysis may occur following inferior alveolar, posterior superior alveolar, or retromandibular nerve blocks. ⁶ In these cases, anesthetic diffusion into the parotid gland or adjacent spaces is thought to impair function of the facial nerve temporarily. The typical presentation involves immediate-onset ipsilateral facial droop that resolves within several hours, supporting a mechanism of anesthetic-induced neuropraxia rather than direct axonal injury. ⁶

Across specialties, including dermatology, otolaryngology, and dentistry, a consistent pattern emerges: transient facial paralysis after local anesthetic injection is rare, self-limited, and typically resolves without intervention. The absence of pain, progressive weakness, or systemic symptoms helps differentiate benign neuropraxia from more concerning causes of facial palsy, such as infection, hematoma, or surgical trauma.

Our case adds to this growing body of literature by illustrating a rare, benign complication following MMS to the conchal bowl. Given the anatomical proximity of this site to the tragus and the facial nerve’s main trunk, we suspect that local anesthetic, despite routine infiltration technique, diffused into nearby fascial spaces and transiently impaired nerve conduction. The patient’s complete resolution of symptoms by the time of discharge further supports a diagnosis of short-lived anesthetic neuropraxia.

To minimize the risk of this complication, dermatologic surgeons should consider the following preventive strategies: use of the lowest effective volume of anesthetic, slow injection under direct visualization, superficial infiltration when possible, and awareness of facial nerve course in high-risk areas. ⁷ Although rare, the potential for transient facial paralysis should be discussed with patients preoperatively, particularly when surgery is performed on or near the tragus, conchal bowl, or preauricular skin. Doing so not only prepares patients but also reduces anxiety should symptoms occur.

Conclusion

This case underscores an uncommon but benign complication of MMS in the auricular region. Transient facial nerve paralysis due to local anesthetic spread can mimic more serious pathology but typically resolves without treatment. Recognition of this entity is important to prevent unnecessary workup, reassure patients, and guide preoperative counseling.