Inverted Papilloma: Benign Tumor of the Maxillary Sinus

Introduction

The maxillary sinus of the face is the most prominent paranasal sinus and has a volume of 0.33 fluid ounces. It acts as a protective covering for the face, helps in the resonance of the voicebox, and reduces the weight of the facial skeleton.

Inverted papilloma is a non-cancerous (benign) tumor of the maxillary sinus. It is a commonly occurring benign tumor with the potential for local invasion and malignant transformation. It mainly affects middle-aged men (40 - 60 years) and has a higher prevalence in males than females (with a male-to-female ratio of 3.5:1).

What Is the Pathology of Inverted Papilloma?

The pathology of inverted papilloma can be described in three terms: their location, macroscopic appearance, and microscopic appearance.

Location

Inverted papillomas are most often found on the side wall of the nasal cavity, particularly near the middle turbinate and maxillary ostium, although they can occur in other nasal areas. As they grow, they can cause changes in bone structure and sometimes spread into the maxillary sinus. Because of its position, it is common for the normal drainage of the maxillary sinus to be affected, although the formation of mucoceles is infrequent.

Macroscopic Features

Macroscopically, inverted papillomas present as irregular, polypoid masses with varying consistency, typically pink in color and prone to bleeding.

Microscopic Features

Under the microscope, they are seen as strips of respiratory epithelium surrounded by a basement membrane, growing into the underlying stroma in an inverted pattern. They typically contain micro-mucous cysts. About 20% show keratinization, and 10 % show signs of dysplasia.

What Are the Clinical Features of Inverted Papillomas?

Inverted papilloma is similar to many other lesions of the sinonasal (tumors that occur in the nasal cavity or nasal sinuses) cavity. Some of the following clinical features can be seen in these tumors -

• Patients frequently complain of nasal obstruction.

• Patients feel pain in the sinus region on the face.

• Epistaxis or nasal bleeding may be a frequent observation by the patient.

Some patients may show severe nasal congestion without experiencing any of the above-mentioned signs. Also, they may experience changes in the sense of smell (anosmia) over time, accompanied mainly by facial pain.

What Is the Potential of Inverted Papillomas for Local and Malignant Spread?

The majority of inverted papillomas are non-malignant or benign lesions. However, approximately 5 to 15 % of cases of inverted papillomas may give rise to common forms of skin cancers such as squamous cell carcinomas. In addition, inverted papillomas may not distantly metastasize to other body organs. However, they tend to be highly aggressive with the potential for local spread, specifically in the nasopharynx, cranial base, orbit, or middle ear.

Since the lesion always grows inwardly, inverted papillomas cause invasive bone destruction around the paranasal sinuses. They may also impact the region of the orbit (eyes) and the spaces between the brain and the facial sinuses. This may be life-threatening in the long term, especially when they are not diagnosed correctly or left untreated.

How Can Inverted Papillomas Be Diagnosed?

Inverted papillomas can be diagnosed using imaging modalities such as MRI (magnetic resonance imaging) and CT (computed tomography). These methods can be used to visualize the masses in the maxillary sinus more accurately. For example, in MRI imaging, these masses may present as a convoluted cerebriform pattern in T1 and T2 contrast-weighted images, which is a diagnostic sign of inverted papilloma. Sometimes, angiography is also used to detect avascular tumors. Plain radiographs may also not play a vital role in diagnosing inverted papillomas. CT also does not give a significant diagnosis, but it shows the soft tissue mass. Intralesional calcifications may be seen through CT.

What Is the Differential Diagnosis of Inverted Papilloma?

Diagnosing inverted papillomas is challenging for dentists as they resemble many other lesions. Also, they resemble other lesions of sinonasal regions, either with or without polypoid masses, which include:

• Lesions or masses of the nasal cavity and middle meatus.

• Conditions like chronic rhinosinusitis.

• Odontogenic sinusitis.

• Antrochoanal polyp or Killian polyp of the maxillary sinus.

• Certain undefined polyp lesions, such as isolated nasal polyps.

• Benign or malignant tumors of the sinonasal area (certain cancerous or malignant tumors may have the ability to mimic commonly occurring inflammatory lesions).

• Other sinonasal papillomas.

What Is the Management of Inverted Papillomas?

Inverted papillomas of the maxillary sinus are diagnostically challenging because they resemble sinonasal diseases of other origins. Also, these lesions require an adequate and extensive surgical approach for excision.

Some of the methods that can be used to remove this tumor are -

1. Medial Maxillectomy - Surgeons may recommend the surgical procedure known as classical medial maxillectomy in cases where it is tough to approach the papilloma through direct methods. In this procedure, the medial wall of the maxillary sinus is resected along with the inferior turbinate and nasolacrimal duct to remove the tumor completely.

Other traditional surgical methods such as transoral sublabial access, Caldwell-Luc procedure, and Canine-fossa-trephination can also be used.

2. Conservative Endoscopic or Endonasal Prelacrimal Surgical Approach - Nowadays, surgeons mostly use the approach through the endoscopic technique (the conservative endoscopic or endonasal lacrimal surgical approach to the sinus) to excise the tumor. In addition, it improves the long-term prognosis and helps preserve the inferior turbinate and the nasolacrimal duct.

Conclusion:

In conclusion, inverted papillomas are characterized by their unique growth pattern of respiratory epithelium extending into the underlying stroma. Microscopically, they present as ribbons of respiratory epithelium encased in a basement membrane, often accompanied by micro-mucous cysts. Although relatively rare, comprising around 0.5 to 4 % of all sinonasal tumors, they can present diagnostic and management challenges due to their potential for local invasiveness and association with synchronous or metachronous malignancies. Approximately 20 % of cases exhibit keratinization, while 10 % demonstrate dysplasia, underscoring the importance of thorough histopathological examination for accurate diagnosis and appropriate management planning. Despite their benign nature, inverted papillomas require complete surgical excision due to their propensity for recurrence and potential for malignant transformation. Long-term follow-up is crucial to monitor for recurrence and to detect any malignant transformation early, ensuring optimal patient outcomes and quality of life.