Spinal Metastasis Secondary to Salivary Gland Malignancy: Systematic Review of the Literature with an Illustrative Case Report

BACKGROUND: Spinal metastasis from salivary gland malignancies is a rare clinical entity with only several reports in the literature. There is no clear guidance for its optimal management. METHODS: A systematic review was conducted following the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines. Databases including Medline, Cochrane, and Embase were searched for cases of spinal metastasis from major salivary gland malignancies. A case report of spinal metastasis from salivary duct carcinoma at our institution supplemented the review. RESULTS: The review included 19 patients with a mean age of 54 years. Patients exhibited varied histopathological subtypes with acinic cell carcinoma and adenoid cystic carcinoma being the most common histopathology. Metastasis appeared from 0 to 35 years after primary diagnosis, with a mean of 11 years. The thoracic spine was most commonly affected (63%), followed by the lumbar spine (33%). Most metastases were osteolytic (79%). Vertebral body involvement was seen in 89% of cases, with significant collapse in 37%. Surgical management was required in 79% of cases, often combined with radiotherapy (63%) and chemotherapy (26%). Surgery generally led to neurological improvement in 80% of cases. CONCLUSIONS: Spinal metastasis from salivary gland malignancies necessitates a comprehensive and multidisciplinary treatment approach due to the complex nature and variability in presentation. Long-term follow-up is essential for early detection and management of spinal metastases given the extended latency period observed in many cases. The potential for metastasis is not solely dependent on tumor grade, emphasizing the need for ongoing vigilance in all patients with salivary gland malignancies.