Definition
• Solitary exophytic endobronchial tumor with fibrovascular stalks covered by stratified squamous epithelium
Clinical features
Epidemiology
• Uncommon
• Middle-aged adults; usually male
Presentation
• Asymptomatic or obstructive symptoms
• Exophytic or dome-shaped mucosal-based nodule can be seen on bronchoscopy
Prognosis and treatment
• Excellent prognosis with complete excision or cryotherapy
• May recur if incompletely excised
• Low malignant potential for cases with atypia/dysplasia
Pathology
Histology
• Exophytic or nodular/inverted mucosal-based arborizing papillary fronds with fibrovascular cores lined by keratinizing squamous epithelium
• Features of viral infection with human papillomavirus (HPV), including nuclear hyperchromasia, koilocytic change, and binucleation, are often present
• Nuclear atypia and dysplasia have been found in these lesions
Immunopathology/special stains
• In situ hybridization for HPV: types 7 or 11 in uncomplicated cases; types 16 or 18 in cases with atypia or dysplasia
Main differential diagnoses
• Squamous cell carcinoma: look for stromal and angiolymphatic invasion
• Papillary adenocarcinoma: usually peripheral; look for invasion and glandular differentiation
• Papillary adenoma: glandular lining of papillary fronds; not mucosal-based
Fig 1 Squamous papilloma. At low power, fibrovascular cores covered by squamous epithelium are seen in this squamous papilloma.
Fig 2 Squamous papilloma. The squamous epithelium is orderly, and no inflammation is present in the fibrovascular core.
Fig 3 Squamous papilloma. The effects of HPV infection, including koilocytic changes and binucleation, are seen in this squamous papilloma.