Collision tumor of small cell carcinoma and squamous cell carcinoma of the maxillary sinus: Case report.

A collision tumor refers to the coexistence of two diagnostically distinct tumors in a common anatomic space. Collision tumors are rare in the oral and maxillofacial region. The present study reported on the case of an 82-year-old female with a collision tumor in the maxillary sinus consisting of small cell carcinoma (SmCC) and squamous cell carcinoma (SCC). Computed tomography (CT) imaging revealed a mass in the right maxillary sinus. The lesion exhibited heterogeneous low signal intensity (SI) on T1-weighted imaging (T1WI), high SI on short T1 inversion recovery and heterogeneous solid enhancement on contrast-enhanced T1WI. The histopathology result of a biopsy specimen confirmed SmCC. After the patient received a course of chemoradiotherapy, follow-up CT revealed a residual tumor. In a second surgery, a remaining tumor and histopathology revealed SCC with no evidence of SmCC. The final diagnosis was a collision tumor made up of SCC and SmCC.