Sinonasal Inverted Papilloma Arising After Endoscopic Sinus Surgery for Inflammatory Polyps

Significant Statement

The case describes a recurrence of sinonasal inverted papilloma (SNIP). It illustrates the diagnostic challenge of distinguishing inflammatory polyps from SNIP. It underscores the value of computed tomography (CT)/MRI in diagnosis. It also demonstrates the importance of endoscopic resection of the tumor base and long-term follow-up. More importantly, this case raises an important clinical question: did the current SNIP represent recurrence of primary disease, or de novo oncogenesis within chronically inflamed mucosa?

Case Presentation

A 52 year-old woman presented to our hospital on April 15, 2024, with a 2-month history of progressive right nasal obstruction and intermittent epistaxis. She denied facial pain, hyposmia, or visual changes. She had undergone bilateral endoscopic sinus surgery at our institution for chronic rhinosinusitis with nasal polyps 6 years ago, and the pathology was reported as inflammatory polyps (Figure 1A and C). The sinus mucosa showed complete epithelialization 2 months after surgery, but this patient was subsequently lost to follow-up until symptom recurrence. She had no history of hypertension, diabetes, or drug allergy.

Figure 1.

Endoscopy showed right maxillary sinus lesion diagnosed as inflammatory polyp by histopathology 6 years ago (A, C), but SNIP at 2024 (B, D).

Physical examination revealed a papillary mass filling the right maxillary sinus and extending into the nasal cavity and nasopharynx, with contact bleeding. Compared to CT 6 years before (Figure 2A-C), soft-tissue mass could be seen in the right maxillary sinus, nasal cavity, and nasopharynx (Figure 2D-F). MRI (Figure 2G-I) demonstrated isointense T1 and mildly hyperintense T2 signal, with heterogeneous gadolinium enhancement. Squamous cell carcinoma antigen was 1.30 ng/mL (reference <1.50 ng/mL). However, this mass was diagnosed as an inverted papilloma by biopsy.

Figure 2.

Axial, coronal, and sagittal images showing soft-tissue mass of right maxillary sinus by CT 6 years ago (A-C) and at 2024 (D-F), and “convoluted cerebriform pattern” of the mass by enhanced MRI (G-I).

Under general anesthesia, complete endoscopic resection was performed via a pre-lacrimal recess approach. The base of the inverted papilloma was found in the antero-inferior portion of the maxillary sinus, yet the base was removed, and the hyperostotic bone was drilled away. Final pathology confirmed SNIP without dysplasia or carcinoma (Figure 1B and D). After 12 months, endoscopy images (Figure 3) showed no residual or recurrent disease.

Figure 3.

Examination shows no evidence of residual or recurrent by 0° and 70° nasal endoscope (A, B).

Discussion

The index of suspicion should be high whenever a patient presents with unilateral nasal obstruction or epistaxis. SNIP appears as a firm and friable mass that bleeds readily on contact, in contrast to the pale, edematous, and avascular appearance of inflammatory polyps. ¹ Imaging is critical to distinguish SNIP from inflammatory polyps and to define the tumor base. CT typically reveals a soft-tissue mass withadjacent hyperostosis or focal bone erosion that marks the attachment site, referred to as “osteitic sign.” MRI further refines the diagnosis: T2-weighted sequences often show a “convoluted cerebriform pattern” whose gyri converge toward the tumor origin. ² However, these imaging hallmarks are mostly absent in an inflammatory polyp. Recently, AI-driven analysis of endoscopy or imaging has substantially improved the diagnostic accuracy of SNIP. More importantly, obtaining multiple targeted biopsies for pathology optimizes the diagnosis of SNIP.

The CT from 6 years ago was reviewed, and no osteitic area was found. This is similar to the literature findings that not all inverted papillomas exhibit the classic osteitic sign on CT. Yet this phenomenon is really a challenge to distinguishing between inflammatory polyps and inverted papilloma. In our case, the absence of typical osteitis, coupled with a failure to obtain tissue from multiple sites, led to the erroneous diagnosis of nasal polyps. So, this experience shows the need to keep in mind that inverted papilloma should not be ignored when we evaluate patients with inflammatory polyps.

Complete surgical removal is the cornerstone of management. Over the past 2 decades, endoscopic resection has supplanted open approaches for most lesions. Meta-analyses report recurrence rates of 12.8% for endoscopic surgery versus 16.58% for external procedures. ³ Yet recurrence is strongly stage-dependent as reported in a multicenter analysis. Cohort of 608 patients followed for a mean of 5 years after surgery, recurrence rates by Krouse stage were 0% (T1), 4.0% (T2), 13.4% (T3), and 36.4% (T4). ⁴ Intraoperative frozen-section analysis of surgical margins and removal of the underlying bone at the attachment site have been shown to further reduce recurrence. Long-term surveillance is essential, for the time to recurrence followed a bimodal distribution with 57% cases recurring within 24 months and 43% from 40 to 103 months. ⁵

This case raises an important clinical question: did the current SNIP represent recurrence of primary disease, or de novo oncogenesis within chronically inflamed mucosa? Yet inflammatory polyps and SNIP may appear similar, and loss of follow-up may allow disease progression. Retrospective re-examination of the original pathology in multipoint may clarify whether dysplastic or papilloma elements were initially missed. In this case, SNIP was most likely the recurrence of a lesion that had been misdiagnosed as an inflammatory polyp. Chronic inflammatory stimuli and human papillomavirus (HPV) infection after surgery may also promote this recurrence. Anyway, we should conduct a more intensive and prolonged surveillance for this patient from now.

Conclusion

There is a great challenge in the initial diagnosis and management of SNIP. High index of suspicion, generous tissue sampling, complete surgical removal, and long-term endoscopic follow-up are essential to optimize the outcomes.