Differences in Imaging and Histology Between Sinonasal Inverted Papilloma with and Without Squamous Cell Carcinoma.

Objectives

Sinonasal inverted papilloma (SNIP) is a rare benign tumor that has potential for malignant transformation, usually into squamous cell carcinoma (SCC). The pre-operative differentiation between SNIP and SNIP-SCC is essential in determining the therapeutic strategy, but it is a challenge, as biopsies may fail to recognize the malignant part of the tumor. Further, a SNIP can also be locally aggressive and thus mimic a malignant tumor. This retrospective study compares the pre-operative differences in computed tomography (CT) and histologic findings between patients with a benign SNIP and those with a SNIP-SCC.

Methods

Eight patients with SNIP-SCC were selected from the hospital registries of the Department of Otorhinolaryngology, Helsinki University Hospital (Helsinki, Finland). For each case a comparable SNIP case without malignancy was selected. Five histopathologic samples of both the SNIP and SNIP-SCC tumors were retrieved. CT images and the histopathologic samples were re-evaluated by two observers.

Results

The nasal cavity and ethmoid and maxillary sinuses were the most common sites for both tumor types. The SNIP tumors were mostly unilateral, and the SNIP-SCC tumors were both unilateral and bilateral. Only SNIP-SCC tumors demonstrated bone defects and orbital or intracranial invasion. Dysplastic findings such as dyskeratosis, nuclear atypia, and maturation disturbances were seen only in the SNIP-SCC tumors.

Conclusions

Bony destruction and invasion of adjacent structures in pre-operative CT images seem to be pathognomonic signs of SNIP-SCC based on this series. To differentiate between SNIP and SNIP-SCC tumors all available pre-operative investigations are warranted.