Difficult preoperative definitive diagnosis of adenoid cystic carcinoma in the parapharyngeal space: A case report

There are few reports in the literature on adenoid cystic carcinoma in the parapharyngeal space; in Japan, only eight cases have been reported to date. We encountered an early case of adenoid cystic carcinoma in the parapharyngeal space. The patient was a 63-year-old woman. On physical examination of the neck, the tumor was not palpable, but computed tomography （CT） and magnetic resonance imaging （MRI） revealed an oval shaped tumor measuring 18×25×26mm located in the left parapharyngeal space. The tumor margin was clearly defined but the boundary between the tumor and the parotid gland was partially indistinct. Moreover, the fatty tissue that typically occupies the parapharyngeal space was completely absent. The external carotid artery was compressed against the anterior border of the sternocleidomastoid muscle but there was no obvious vascular invasion of the tumor. Our preoperative diagnosis was suspected schwannoma based on tumor location and morphology, and CT and MRI findings. The tumor was removed using the trans-cervical approach. The fibrous funicular fragment was adherent to its germinal pole and extended toward the base of the skull. After we confirmed that there was no tumor substance in this fragment, we excised this fragment and removed the tumor. Pathological examination revealed the tumor to be adenoid cystic carcinoma. If we had suspected that adenoid cystic carcinoma could also occur in the parapharyngeal space, we might have performed 18-fluoro-deoxyglucose positron emission tomography or fine needle aspiration biopsy preoperatively. Regarding the treatment, if the possibility of malignancy had been considered, the trans-parotid approach or mandibular swing method would have been the optimal curative treatment. Should the tumor recur, we will perform extensive resection involving the facial or another cranial nerve depending on the location of recurrence, in addition to radiation therapy.