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Sinonasal polyposis

Sinonasal polyposis presents clinically with progressive nasal obstruction, rhinorrhea, facial pain, headache, and anosmia, and is imaged to assess the extent of polypoid disease and associated complications in the nasal cavity and paranasal sinuses.

Key Images

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Look For First
  • Multiple hypoattenuating polyps completely filling and obliterating the nasal cavity and paranasal sinuses on CT
  • Truncation of the middle turbinate with polyps extending beyond the middle meatus
  • Opacified ethmoid sinuses with convex lateral walls and attenuated sinus walls rather than gross sinus expansion
Key Image Findings
  • On CT, extensive mucosal polyps occupy and obliterate the nasal cavity and paranasal sinuses, typically appearing hypoattenuating but occasionally hyperattenuating if increased protein content or fungal infection is present.
  • Benign bone remodeling or erosion occurs at the site of polypoid mass effect, distinguishing polyps from mucoceles which cause entire sinus expansion.
  • Enlargement of the infundibula and attenuation of ethmoid sinus walls and nasal septum are characteristic features.
  • The inferior nasal meatus is occasionally spared, while the middle turbinate becomes truncated by the polypoid mass.
  • Opacified ethmoid sinuses demonstrate convex lateral walls and may contain gas-fluid levels from associated sinusitis.
  • Associated fungal sinusitis may be present concurrently, and Woakes syndrome represents severe recalcitrant disease with nasal pyramid deformity.
  • Osseous metaplasia can occur as a complication of chronic polyposis.
  • The Meltzer grading system (0-4) clinically classifies polyposis from no disease to complete nasal cavity obstruction.
Differential Diagnosis
  • Sinonasal retention cyst: can be radiographically indistinguishable from polyps but typically spares the nasal cavity proper, remaining confined to the sinuses.
  • Allergic fungal sinusitis: commonly associated with polyps but shows hyperattenuating central areas and low T1/T2 signal on MRI due to fungal colonization.
  • Granulomatosis with polyangiitis: centers in the nasal cavity but can be distinguished by clinical and serological findings.
  • Mucocele: causes expansion of the entire sinus rather than localized remodeling/erosion, helping differentiate from polyps.
  • Antrochoanal polyp: solitary polyp extending into the nasopharynx, unlike the multiple bilateral polyps of sinonasal polyposis.
Discussion

Sinonasal polyps are formed by influx of fluid into the lamina propria of the Schneiderian mucosa, resulting in benign mucosal proliferation.

Polyps are the most common expansile lesions of the nasal cavity and occur predominantly in adults, being rare in children.

Chronic sinusitis results from obstruction of sinus drainage pathways, perpetuating polypoid disease through inflammation.

Multiple conditions are associated with polyps including infectious rhinosinusitis, cystic fibrosis, allergic fungal sinusitis, asthma, nickel exposure, and eosinophilic granulomatosis with polyangiitis.

Aspirin-exacerbated respiratory disease (AERD) represents an important clinical complication to recognize.

The distinction between polyps and mucoceles is crucial as polyps cause focal remodeling while mucoceles cause global sinus expansion.

Reporting Pearls

Describe the extent using the Meltzer grading system and specify whether polyps are confined to the middle meatus, extend beyond it, or cause complete nasal obstruction; note any bone remodeling versus erosion, which confirms benign polypoid disease rather than mucocele or mass lesion.

Pitfalls
  • Confusing sinonasal polyps with retention cysts: retention cysts typically spare the nasal cavity while polyps fill it.
  • Missing the diagnosis of concurrent allergic fungal sinusitis by not appreciating hyperattenuating areas and low signal on MRI sequences.
  • Overinterpreting bone erosion or remodeling as aggressive disease when benign remodeling is expected in chronic polyps.
  • Failing to assess for associated complications such as osseous metaplasia or aspirin-exacerbated respiratory disease.
Source: Reference source

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