Researchers report a case of iatrogenic injury to the parotid duct after Mohs' surgery micographic for a squamous cell carcinoma in the left jaw excision region, Treated by injection of botulinum toxin type A . Although the fistula by duct injury can be self-limiting, botulinum toxin injection by promoting the inactivity of the salivary gland allows rapid healing of the fistula .

The onset of salivary fistula post-parotidectomy occurs in 4-14% of the cases, the majority of which are self-limiting and respond well to conservative treatment. Several techniques have been employed to treat this complication: percutaneous aspiration, compression bandage, anticholinergic drugs, radiation therapy, botulinum toxin, and surgical repair.

This report presents a parotid duct iatrogenic lesion case, which occurred after Mohs' micrographic surgery (MMS) recommended for squamous cell carcinoma (SCC) excision in the left mandibular region, treated with the injection of type A botulinum toxin (BoNT-A).

A 79-year-old male patient displayed a tumor measuring 2.5 x 2.3 cm, with an ulcerated center, in the left mandibular region, and with skin retraction in the area below the lesion. The biopsy indicated SCC, and the pre-surgery ultrasound exam identified the muscular plane had been affected.

Botulinum toxin is known for releasing acetylcholine at the autonomic nervous system's cholinergic synapses. Because of this effect, it has been used for treating sialorrhea cases in Parkinson's disease, post-stroke, and in refractory post-parotidectomy parotid fistula cases. The BoNT-A doses vary between 10 and 100U.

Lim and Choi reported solving an acute fistula case after a parotid tumor resection with the use of 10U of BoNT-A. Two cases of BoNT-A application to treat parotid duct lesions caused by facial SCC resection are described in literature.

Hatzis and Finn described the case of a 58-year-old male patient who, after undergoing the excision of SCC on the left mandibular area, developed a salivary fistula on the 6th day after surgery. He was initially treated with 200U of BoNT-A (Botox®, Allergan, Inc.), followed by an additional 100U five days later. The fistula was fully resolved after a 21-day period.7

Krishnan et al. reported the case of a 62-year-old male patient who, after removal of right malar region SCC, exhibited the formation of persistent sialocele on the 5th day after surgery and was treated with ultrasound guided BoNT-A injections. Application was made at three parotid gland points, with a total dose of 23U, and the condition was solved after two weeks.

In this study's case, the fistula was treated with 32U of BoNT-A in two applications. The first application of 16U with an 8 mm needle presented no improvement, and a second application of 16U with a 40mm needle was performed after seven days. The authors believe that the short needle did not reach the salivary gland.