Spontaneous regression of pseudotumor inflammatory parotitis: case presentation and literature review

Background: Pseudotumor inflammatory sialadenitis (PIS) is a rare disease. The differential diagnosis relays mainly on histopathology. We believe this is the first case of spontaneous regression of pseudotumor parotitis. Case presentation: A 58-year-old male patient with a history of diabetes and hypertension presented a huge mass of the parotid gland suggesting an advanced stage malignancy. CT scan disclosed a large parotid tumor that invaded the parapharyngeal space and invaded the internal carotid artery in the parapharyngeal space. Complete surgical removal was therefore impossible. A biopsy was planted for further management according to the tumor board's recommendations. Within 5 weeks from the initial consultation, the tumor has completely and spontaneously resolved. The patient presented late to his biopsy appointment due to COVID free circulation restriction as he lived in another city. Furthermore, the workup ruled out autoimmune disease, viral-induced parotitis, inflammatory myofibroblastic tumor, and immunoglobulin G4- related inflammatory pseudotumor. Parotid gland biopsy revealed nonspecific fibrosis tissue. The patient remains free of disease without further treatment for a year follow-up. Conclusions: Inflammatory pseudotumor parotitis is a manifestation of many conditions, few have been identified such as inflammatory myofibroblastic pseudotumor and immunoglobulin G4-related inflammatory pseudotumor but many remain unknown. Meticulous clinical and imaging, biology, immuno-pathology work-up is crucial for differential diagnosis.