A Case of Accessory Nerve Schwannoma Extending to the Hypoglossal Canal and Mimicking Hypoglossal Nerve Schwannoma

Introduction: Schwannomas constitutes 8% of primary intracranial tumors, and 2% of these are considered to be jugular foramen schwannomas originating from the lower cranial nerves (IX, X, XI). Among them, accessory schwannoma is very rare. We experienced a case in which a patient was diagnosed with hypoglossal schwannoma preoperatively but was later diagnosed with accessory schwannoma based on intraoperative findings, and we report this case.

Materials and Methods: A 62-year-old female. Three years ago, she was diagnosed with dysarthria and right-sided tongue deviation and atrophy, and a head MRI revealed a 17-mm tumorous lesion on the dorsal side of the right internal carotid artery (ICA) that appeared to be progressing from the right hypoglossal canal. She was referred to our department with a suspected hypoglossal schwannoma. Although surgical treatment was proposed, the patient requested follow-up observation, and three years later, she began to develop dysphagia, hoarse voice, and atrophy of the right trapezius muscle was observed. The tumor had grown to 30 mm in size, and surgery was recommended. Preoperative MRI showed that the tumor had progressed extracranially to the first cervical vertebra (C1). CT showed enlargement of the right hypoglossal canal, and tumor removal was planned by opening the hypoglossal canal via a transcondylar approach. Intraoperative findings confirmed the tumor capsule at the C1 level, and bone removal was performed to open the hypoglossal canal. However, no lesions were found that were continuous with the tumor confirmed at the C1 level, and the tumor was found to be continuous with the jugular foramen. When the intradural examination was performed, the hypoglossal nerve was normal, and a tumorized accessory nerve was found, leading to a diagnosis of accessory nerve schwannoma. The tumor within the jugular foramen and the extracranial tumor were completely removed within the capsule, and the surgery was completed. Postoperatively, the tongue deviation improved.

Discussion: Hypoglossal nerve paralysis-induced tongue atrophy and tongue deviation are observed in 78.7 to 92% of patients with hypoglossal nerve schwannoma. Julow et al classify accessory nerve schwannoma into intrajugular and intracisternal types based on the site of origin. Intrajugular type schwannoma presents with jugular foramen syndrome (tinnitus, hearing impairment, dysphagia, and hoarseness) and may show enlargement of the jugular foramen on CT scans. In this case, the patient presented with hypoglossal nerve paralysis and MRI findings suggested the extension of a tumor lesion to the hypoglossal canal, so the preoperative diagnosis was hypoglossal nerve schwannoma. However, intraoperative findings did not reveal tumor in the hypoglossal canal, which caused confusion during surgery. Monden et al stated that in cervical schwannoma, glossopharyngeal nerve and hypoglossal nerve lesions compress ICA dorsally, while accessory nerve lesions compress it ventrally or laterally. In this case, ICA was compressed ventrally. Furthermore, the expansion of the hypoglossal canal was found only the extracranial side and was integrated with the jugular foramen. It can be difficult to differentiate between jugular foramen schwannoma and hypoglossal schwannoma based on the initial symptoms, so it is important to conduct a thorough image examination and consider the possibility of both.

Publication History

Article published online:
07 February 2025