The inverting Schneiderian papilloma has been recorded in the medical literature for more than a century and remains a topic of controversy.1 It is generally accepted that inverting papilloma is a benign tumor of the sinonasal tract mucosa that is locally aggressive and has significant malignant potential. It is an uncommon lesion in which proliferated epithelial reserve cells invert into the underlying stroma rather than growing outwardly from the surface.² Inverting papilloma is derived from sinonasal (Schneiderian) mucosa, formed from the invaginating ectoderm of the olfactory plates at the end of the fourth week of embryonic life.¹ The neoplastic epithelium may be of a respiratory, transitional, or squamous type. Inverting papillomas most often arise from the lateral nasal wall in the area of the middle turbinate and may extend into the maxillary and ethmoid sinuses. In most cases, this slow-growing tumor is unilateral.³

Inverting papillomas are unique, characterized by their capacity to destroy bone by pressure erosion.⁴ They are also associated with squamous cell carcinoma and have a tendency to recur if incompletely excised. Lesperance and Esclamado⁵ retrospectively found squamous cell carcinoma with inverting papillomas in 27% of cases in their study.

Questions that remain unanswered regarding inverting papilloma include its etiology, malignant potential, and appropriate management.

Background

Inverting papilloma was first described by Ward in 1854 and by Billroth in 1855. Kramer and Som in 1935⁶ distinguished the disease from inflammatory polyps.

Because of the infrequent occurrence of the lesion, an appropriate name has not yet been agreed upon. At least 20 different terms have been used in referring to this lesion.⁷ Such terms as papillary sinusitis or epithelial papilloma do not reflect the seriousness of the lesion. Conversely, such expressions as papillary carcinoma or villous cancer are perhaps overly threatening and can lead to overly aggressive treatment measures.⁸

Epidemiology

The overall incidence of inverting papillomas varies from 0.5% to 4% of all primary nasal tumors.¹ They are three times more common in men than in women. Whites have a higher incidence than blacks. Papillomas are rarely found in childhood and adolescence and are seen primarily in the 40- to 70-year-old age group, with a peak incidence during the sixth and seventh decades of life.⁸

Etiology

The etiology of the lesion is uncertain. Chronic infection, allergy, tobacco, and occupational exposures are unlikely etio-logic factors, as inverting papillomas are usually unilateral.¹ Several studies using in situ hybridization have demonstrated the presence of human papillomavirus (HPV) DNA. Types 6b and 11 were isolated in inverting papillomas in 76% of cases in a study conducted by Weber et al.⁹ Epstein-Barr virus (EBV) has also been implicated.

Diagnosis

Patients with inverting papilloma usually present with unilateral nasal obstruction, sinusitis, epistaxis, and rhinorrhea. Physical examination shows a unilateral mass, which frequently resembles a bleeding inflammatory polyp. Inflammatory polyps are usually bilateral; consequently, the presence of a unilateral polyp raises suspicion of the presence of an inverting papilloma. The diagnostic workup includes computed tomography (CT) or magnetic resonance imaging (MRI) of the sinuses as well as biopsy. CT delineates whether there is septal deviation, bone erosion, intracranial extension, or opacification of the nasal cavity and sinuses. MRI is useful for distinguishing tumor from mucosal inflammation and mucus secretions. Imaging studies should precede biopsy in patients suspected to have encephaloceles. Although clinical and radiologic suspicion of an inverting papilloma may be high, an adequate biopsy for tissue diagnosis must be obtained before proceeding with definitive management. Biopsy serves not only to confirm the diagnosis, but also to rule out associated squamous cell carcinoma.

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