Sinonasal ameloblastoma is an extremely rare neoplasm. Herein we present a case of sinonasal ameloblastoma and discuss its histogenesis and related morphological characteristics. An 80 years-old Japanese male had a polypoid mass initially diagnosed as a nasal polyp. A prior biopsy was interpreted as a salivary gland-type tumor and he was therefore referred to a regional general hospital for surgical removal of the lesion. Preoperative contrast-enhanced magnetic resonance imaging revealed a space-occupying lesion in the right nasal cavity and the right maxillary sinus with poor contrast enhancement. Histopathological findings revealed that the tumor consisted of follicular/plexiform-like cell nests with peripheral palisading, extending continuously to the adjacent mucosa. A recurrent polypoid mass accompanied by bone destruction of the maxillary sinus was found two years after the surgery, but it was left untreated. Although sinonasal ameloblastoma remains under-recognized, its characteristics, including its histopathological features, need to be more widely known to allow its correct diagnosis and adequate management.
Sinonasal ameloblastoma (SA) is an extremely rare neoplasm.
SA is definitely originated from sinonasal mucosal epithelium.
SA should be distinguished from gnathic ameloblastoma beyond the cortex.
Sinonasal ameloblastoma (SA) is an extremely rare neoplasm. Schafer et al. conducted the first detailed clinicopathological analysis of SA based on 24 cases in 1998 [ ]. The fourth edition of the World Health Organization (WHO) classification of head and neck tumors in 2017 first described SA with reference to its definite mucosal epithelium-derived histogenesis, unlike the third edition in 2005, which simply noted that it was rare in the sinonasal tract and nasopharynx. Several cases presenting with a nasal polyp-like appearance have recently been described, but not all have included full histopathological examinations [ , ], and one was derived from the maxillary bone extending beyond the cortex to the nasal cavity [ ]. Herein we present a case of SA with a focus on its histogenesis and related morphological characteristics.
The patient was an 80 years-old Japanese male, who had a polypoid mass initially diagnosed as a nasal polyp. A prior biopsy had been interpreted as a salivary gland-type tumor, and he had been referred to a regional general hospital. Preoperative contrast-enhanced magnetic resonance imaging revealed a space-occupying lesion in the right nasal cavity and the right maxillary sinus with poor contrast enhancement. There were no confirmed intraosseous lesions of the maxilla or bone destruction throughout ( Fig. 1 a–c). A malignant tumor was considered unlikely on the basis of clinical observations. Surgical removal of the lesion was performed along with curettage of the surrounding tissue. During the outside follow-up observation, a polypoid mass measured approximately 2cm in diameter was found two years after the surgery, which was accompanied by wide destruction in bony wall of the maxillary sinus adjacent to its base in CT scan ( Fig. 1 d and e). The biopsy specimen revealed a recurrent lesion quite identical to the primary tumor, but it was left untreated, as the patient did not hope further radical treatment. Final outcome was not available.
Gross examination revealed a polypoid mass covered by normal mucosa, sampled in fragments ( Fig. 1 f). Microscopy revealed a lesion composed mainly of basaloid cells and associated with numerous cystic structures containing eosinophilic fluid ( Fig. 2 a). Most tumor cells had darkly stained nuclei and scant cytoplasm and were ovoid or columnar in shape. Some cells with clear cytoplasm were also found. The tumor exhibited a predominantly follicular and plexiform arrangement with nuclear palisading of columnar or cuboidal cells beneath the mucosa ( Fig. 2 b and c). Within the follicular nests, polyhedral squamoid cells showed a loose dissociated arrangement resembling the stellate reticulum of the enamel organ ( Fig. 3 a). Cellular atypia was generally inconspicuous and mitotic figures were rare ( Fig. 3b ). No invasive growth or bone destruction was identified.