Inverting papilloma is a benign sinonasal tumour typically found in older-aged adults, characterised by its endophytic growth pattern and often presents as a unilateral nasal obstruction.
Description
Inverting papilloma, also known as Schneiderian papilloma, is a benign but locally aggressive tumour originating from the Schneiderian membrane, which lines the nasal cavity and paranasal sinuses.
Pathogenesis
The exact pathogenesis remains unknown, though human papillomavirus (HPV), particularly type 6 and 11, has been implicated in some cases.
Epidemiology, Risk Factors & Associations
- More common in males than in females (ratio 4-5:1)
- Predominantly affects adults in their 5th to 7th decade
- Strong association with smoking
- Possible association with HPV types 6 and 11
Clinical Features
- Often presents with unilateral nasal obstruction, epistaxis, and rhinorrhea
- May cause facial pain or pressure, and loss of smell in some cases
Complications
Inverting papilloma, although benign, can be associated with a number of complications due to its location and propensity to recur. These include:
- Malignant transformation: This is the most significant complication. There’s a risk of transformation into squamous cell carcinoma, which is reported to occur in about 5-15% of cases. This risk is increased in cases with dysplasia or carcinoma in situ.
- Recurrence: Even after surgical removal, inverting papillomas have a relatively high recurrence rate, reported to be around 20-50%, especially if the removal is incomplete.
- Sinonasal obstruction: Due to the mass effect of the growing tumour, it can lead to obstruction of the nasal passages causing symptoms like nasal congestion, difficulty breathing, or sinusitis.
- Bone erosion: Although benign, inverting papillomas can cause bone erosion due to pressure effects, particularly when large or long-standing.
- Intracranial extension: In rare cases, the papilloma can erode through the skull base and extend into the intracranial cavity, leading to serious complications like meningitis or cerebrospinal fluid leak.
Pathological Features
Histopathology
- Gross: Lesion appears as a bulky polypoid, often friable mucosal mass with red-gray colour and lobulated surface. May be multifocal. Can extend through septum.
- Microscopic: Characterised by an endophytic (inward) growth of columnar epithelium with goblet cells, along with a fibrovascular core. Folds into the underlying stroma without disruption of the underlying basement membrane.
Radiological Features
CT
- Shows a unilateral soft tissue mass often originating from the lateral nasal wall or sinus
- May have bony remodeling, thinning, or even destruction due to its locally aggressive nature
MRI
- T1: Isointense to hypointense
- T2: Hyperintense
- Contrast enhancement: Strong enhancement due to high vascularity
Grading and Staging
Given its benign nature, a traditional cancer staging system does not apply to inverting papilloma. However, the Krouse staging system is used to categorise the extent of the disease.
Diagnosis
Diagnosis is usually made via nasal endoscopy and biopsy.
Differential Diagnosis
- Squamous cell carcinoma: May have associated necrosis, higher age of presentation, and more aggressive features on imaging
- Sinonasal polyps: Usually bilateral, associated with chronic sinusitis
- Juvenile angiofibroma: Seen in adolescent males, has a characteristic vascular pattern on imaging
Management
Surgical resection is the mainstay of treatment due to its locally aggressive nature and the potential for malignant transformation (around 5-15% of cases). Regular surveillance post-surgery is recommended due to the high recurrence rate.