A 47-year-old woman came to our department 3 months after discovering a tumour in the left preauricular region. The patient reported that the lesion was of sudden onset and progressive growth. She complained of pain in the temporal, cervical and left periocular region. Her medical history included only essential arterial hypertension and treatment with angiotensin-converting enzyme inhibitors, with no other relevant systemic alterations.
Physical examination revealed a nodule approximately 1.5 cm in diameter in the left preauricular region. On palpation, the tumour was soft, mobile and slightly tender to the touch. The maximum oral opening is 45 mm and there is joint popping in both joints. The rest of the head and neck examination is unremarkable.
Computed tomography (CT) and magnetic resonance imaging (MRI) reveal an image suggestive of a cystic lesion measuring 1.8 × 1.7 × 1.4 cm adjacent to the upper border of the parotid gland. The MRI shows a left TMJ-dependent pedicle, with the position of the articular meniscus and displacement of the mandibular condyle with open and closed mouth being normal.

A fine needle aspiration puncture was performed, which was reported as a sample consisting entirely of proteinaceous material and histiocytes, compatible with a cystic lesion.
In view of the findings obtained, surgical treatment was carried out using a preauricular approach, identifying the trunk of the facial nerve and its respective branches. After dissection of the facial nerve, it was decided to perform a superficial parotidectomy of the upper portion as multiple adhesions to the lesion were found, isolating the synovial cyst above the frontal branch of the facial nerve. Subsequently, the pedicle that communicates the cyst with the temporomandibular joint was visualised, proceeding to its ligation and subsequent resection. The wound was sutured in planes.

The surgical specimen obtained was fixed with 10% formalin. Histological sections stained with haematoxylin and eosin revealed a multilocular cystic lesion. To establish with certainty the presence of synoviocytes in the cyst lining, immunohistochemical analysis confirmed their existence.

During the outpatient follow-up of the patient after 9 months of evolution, she has shown no postoperative complications or signs of recurrence.