Title: The inverted papilloma arising from the cribriform plate of the ethmoid bone
Abstract: A 43-year-old female presented with 12-week history of left-sided otalgia and localized left malar discomfort. Her symptoms were not associated with tinnitus, dizziness nor changes in hearing. The facial pain did not coincide with mouth opening nor dental pathologies. There was no history of recent trauma, no previous otological nor dental surgeries and no history of upper respiratory infections. Clinical examination was unremarkable except for a small botryoid nasal polyp in the left superior meatus identified on nasoendoscopy. A computed tomography (CT) of the sinuses revealed complete opacification of the left posterior ethmoid sinus cells and a mass in the superior meatus alongside demineralisation of the lateral lamella of the cribriform lamina (Fig. 1a). Magnetic resonance imaging (MRI) demonstrated hyperintense mucosal hypertrophy and complete occlusion of the left posterior ethmoidal air cells. Notably, an isointense lesion along the medial wall was identified with alternating isointense and hyperintense bands extending to the postnasal space (Fig. 2). The patient underwent functional endoscopic sinus surgery with stereotactic image guidance for biopsy and complete resection of the lesion. Intraoperatively, a polypoid lesion arising from the cribriform plate and lateral lamella of the cribriform, involving the superior turbinate and extending with broad base to the orbital apex was identified and resected completely. Both the cribriform plate and its lateral lamella bone were preserved. It was decided not to drill these thin bones nor cover the exposed area to allow for surveillance (Fig. 3). Histopathology confirmed the diagnosis of inverted papilloma with predominant endophytic architecture and no evidence of malignant transformation. There were no post-surgical complications and the symptoms immediately improved. The patient was completely tumour free at the 3-month postoperative endoscopy and CT scan (Fig. 1b). Six Follow-ups every six months are planned for surveillance. Inverted papilloma (IP) is the most common, yet locally aggressive, benign epithelial neoplasm of the nasal cavity.1 It is derived from the Schneiderian epithelium lining the paranasal sinuses and is the most common of three subtypes of Schneiderian papilloma, followed by fungiform and cylindrical papillomas.2 IP is estimated to affect 0.6 cases per 100 000 people annually and represents 0.5–4% of nasal tumours.2 It most commonly presents in males in their fifth to seventh decade of life.3 Recurrence can occur in 41% to 78% of cases when incompletely resected, and in up to 14% of cases after complete resection.4 Recurrence more than 5 years after resection occurs in 20% of cases.5 Malignant transformation to squamous cell carcinoma has been reported in between 5% and 15% of cases.4 A recent systematic review revealed that the most common attachment of IP is within the maxillary sinus.6 Intracranial extension is rare and occurs in 1–2% of cases but, when present, the frontal sinus is the most common site of extension comprising 49% of cases, followed by the cribriform plate in 29% of cases.3 The prognosis for intracranial extension of IP depends on the presence of dural invasion and the achievement of complete resection.2 In this report, there was no intracranial invasion but there was involvement of the mucosa overlying the olfactory fossa, and the operative decision to retain the thin bone of the lateral lamella and the cribriform plate of the olfactory fossa was made in order to minimize the risk of both intraoperative cerebrospinal fluid leak and subsequent intracranial invasion. Typically, it would be desirable to remove the underlying bone at the tumour attachment site, however, this dictum should not be universally followed as, given the location of the attachment in this case, bony removal would potentially create an intracranial communication and any local recurrence would come with risk of intracranial extension, therefore, a more extended approach would be required. Resection would also necessitate a mucosal cover which would potentially hide any recurrence and limit potential for endoscopic surveillance. The pathogenesis of IP is still undetermined; however, recent reports suggest that both low- and high-risk human papillomavirus (HPV) are correlated to its development.1 Histopathology is necessary to confirm diagnosis. The characteristic histopathological appearance is of hyperplasic epithelium inverting into the underlying stroma with an intact basal membrane.1, 3 Clinically, the most common presenting complaints are nasal obstruction, epistaxis, nasal discharge, and sinus pressure and pain. Intracranial extension may cause headaches and/or proptosis.3 IP can transverse bony anatomical barriers and cause bone destruction through pressure necrosis. In terms of investigative imaging, a CT scan usually shows hypodense lesions with possible bone erosion and destruction.7 A focal hyperostotic area is strongly correlated with the area of attachment.8 Additionally, on MRI the lesion is typically described as a cerebriform in appearance, which is useful in identifying its extent. The treatment of IP is based on its locally aggressive feature, tendency to recur, and the risk of malignant transformation. With the advancement of endoscopy, the standard treatment for sinonasal IP is transnasal endoscopic resection with identification and extirpation of the attachment site with either a cutting instrument or a drill to eliminate microscopic residual tumour.9 The value in reporting this case is to present circumstances to the reader where removal of the attachment site is both contrary to the safety of the surgical procedure and of benefit to the patient for long-term surveillance without compromising oncologic integrity. This does not negate the need for long term follow-up with extended six-monthly follow-up endoscopic examinations required. MRI is the modality of choice if recurrence is suspected. If recurrence occurs, surgical management would require a wide resection of the skull base combined with neurosurgery to optimize resection and minimize the risk of intracranial extension or recurrence. The management of an inverted papilloma arising from the cribriform plate is challenging and there is paucity in the literature leading to diverse opinions even among experienced rhinologists. Whilst drilling of the bony attachment site is considered mandatory in the current literature, there are cases that require individualization such as at the cribriform plate where this would cause disruption of the skull base, increasing the risk of intracranial extension in recurrent cases. Further, reinforcing the exposed skull base is also suboptimal, as this can prevent surveillance. Open access publishing facilitated by Macquarie University, as part of the Wiley - Macquarie University agreement via the Council of Australian University Librarians. Marina Neves Cavada: Conceptualization; methodology. David James Roshan: Conceptualization. Chetan Ashok Lodhia: Conceptualization; software. Raymond Sacks: Conceptualization; resources; supervision.