Inflammatory pseudotumor of frontal sinus mimicking an aggressive malignancy: a rare case with diagnostic challenge on fine needle aspiration

Abstract

Abstract Introduction/Objective Inflammatory pseudotumor (IPT) of sinonasal tract is a rare disease that sometimes mimicks malignancy in radiographic findings. Diagnosis of IPT on fine needle aspiration (FNA) is challenging due to limited cellularity and lack of architectural evaluation. Methods/Case Report Patient is a 59-year-old female presented with left front head swelling, facial pain and pressure. Imaging demonstrated a 3.0 cm hypermetabolic frontal sinus mass with osseous erosion through the calvaria table and deviating the adjacent dura, suspicious for malignancy. Also, an incidental 6.8 cm renal mass was identified and was proven to be clear cell renal cell carcinoma. FNA from frontal sinus showed loosely cohesive atypical cells with prominent nucleoli and occasional mitotic activity mixed with lymphoplasmacytic inflammation and eosinophils. Extensive immunostains showed that the lesional cells were only weakly stained for CD10 and desmin. Because of prominent cytologic atypia and radiological concerning for malignancy, FNA was diagnosed as malignancy not further classified. The patient underwent frontal sinus resection and the surgical specimen showed spindle cell proliferation surrounded by reactive woven bone with plump osteoblasts in a myxocollagenous stroma containing mixed lymphoplasmacytic cells and eosinophils. The spindle cells are positive for actin and calponin, negative for ALK. The spindle cells and plump osteoblasts corresponded to the atypical cells observed on FNA. The overall finding is consistent with IPT, although inflammatory myofibroblastic tumor cannot be completely ruled out. During follow up, the patient developed metastatic renal cell carcinoma in lung. Her frontal sinus lesion was stable for 17 months after surgery. Results (if a Case Study enter NA) NA Conclusion IPT of sinonasal tract is a rare lesion that sometimes demonstrate aggressive radiologic features. FNA from IPT poses a diagnostic challenge and can be misinterpreted as malignancy due to prominent cytologic atypia. Being aware of this rare entity helps avoid misdiagnosis and triggers the request for core biopsy during onsite evaluation.