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Granulomatosis with polyangiitis

Granulomatosis with polyangiitis (GPA) is a multisystem necrotizing non-caseating granulomatous vasculitis affecting small to medium-sized vessels. Upper respiratory tract involvement is common, presenting with chronic nasal obstruction, rhinitis, and epistaxis, often mistaken for chronic sinusitis over months to years.
Look For First
  • Bony/cartilaginous erosions affecting lamina papyracea, nasal septum, and lateral nasal cavity wall with or without perforation
  • Sclerosing osteitis of the nasal cavity with scalloping, sclerosis, and neo-osteogenesis
  • Nasal saddle deformity or septal perforation indicating destructive bone involvement
  • Enhancing soft tissue nodules or mass-like mucosal lesions in the sinonasal cavity
Key Image Findings
  • On non-contrast CT, sinonasal mucosal thickening with or without air-fluid levels and soft tissue nodules indicates active inflammation and granulomatous disease
  • Bony erosions preferentially involve the lamina papyracea, nasal septum, and lateral nasal cavity wall, which may show perforation—a distinctive feature of GPA that helps distinguish it from simple sinusitis
  • Sclerosing osteitis manifests as scalloping of bone margins, increased bony sclerosis, neo-osteogenesis, and calcification within and around the sinonasal cavity
  • On post-contrast CT, enhancing soft tissue nodules and involved mucosal tissue confirm active granulomatous infiltration and inflammation
  • MRI T1 sequences reveal low-to-intermediate signal intensity nodules or mass-like mucosal lesions, while T1 C+ (Gd) shows enhancement of involved mucosal tissue indicating granulomatous involvement
  • MRI T2 sequences show low signal intensity of nodules relative to the high signal intensity of surrounding inflamed, edematous mucosa, creating a characteristic appearance
  • Subglottic stenosis may develop from lower respiratory tract involvement, visible on both CT and MRI as narrowing of the subglottic airway
  • Lacrimal gland involvement and mastoiditis/otitis may accompany sinonasal disease, reflecting the multisystem nature of GPA
Differential Diagnosis
  • Chronic sinusitis: lacks destructive bone changes and bony erosions; presents primarily with mucosal thickening and air-fluid levels without the aggressive sclerosis and perforation seen in GPA
  • Fungal sinusitis: often shows calcification and heterogeneous signal; typically unilateral; lacks systemic granulomatous involvement; does not cause bone perforation in the pattern seen with GPA
  • Sinonasal polyposis: presents with polypoidal masses without significant bony erosion or perforation; driven by allergic/inflammatory mechanisms rather than vasculitis
  • Sinonasal sarcoidosis: may show nodular mucosal involvement but lacks the destructive bone erosions, osteitis, and perforation characteristic of GPA; sarcoidosis is primarily a granulomatous infiltration without vasculitis
  • Cocaine-induced midline destructive lesion: can cause nasal septal perforation and mucosal ulceration; history of cocaine use and lack of systemic disease features help distinguish from GPA
  • Other causes of nasal septal perforation: trauma, autoimmune conditions (SLE, relapsing polychondritis), and iatrogenic causes lack the associated bony erosions, sclerosis, and sinonasal infiltration pattern of GPA
Discussion

GPA is a necrotizing non-caseating granulomatous vasculitis; the vasculitic component distinguishes it pathologically from isolated granulomatous inflammation seen in sarcoidosis

Upper respiratory tract involvement occurs in the majority of GPA patients and is often the presenting feature, yet diagnosis is frequently delayed because symptoms mimic chronic sinusitis

The combination of aggressive destructive bony changes (erosions, perforations, saddle deformity) with mucosal inflammation and soft tissue nodules is highly characteristic of GPA and helps narrow the differential diagnosis

Sclerosing osteitis—manifested by scalloping, sclerosis, and neo-osteogenesis—is a distinctive finding reflecting the chronic inflammatory and fibrotic response of bone to granulomatous vasculitis

Treatment typically involves corticosteroids and cytotoxic agents such as cyclophosphamide; imaging helps establish baseline disease burden and monitor response to therapy

The disease is generally indolent in the upper respiratory tract but can progress to fulminant disease with secondary sepsis requiring antibiotics in addition to immunosuppressive therapy

Reporting Pearls

When reporting GPA with upper respiratory tract involvement, clearly document the pattern of bony destruction (specifying lamina papyracea, septal, and lateral wall erosions), presence of perforation, associated sclerotic bone changes, and extent of mucosal thickening and soft tissue nodules; this constellation of findings should prompt consideration of GPA and comparison with prior imaging or clinical correlation for systemic disease manifestations.

Pitfalls
  • Misinterpreting aggressive bony erosions and septal perforation as simple chronic sinusitis, leading to delayed diagnosis; always consider GPA when seeing erosive changes beyond typical infectious or allergic sinusitis
  • Focusing only on mucosal thickening and missing the more specific finding of bony/cartilaginous erosion and sclerosing osteitis, which are key to raising the diagnosis
  • Failing to recognize nasal saddle deformity or septal perforation as a sign of systemic disease requiring clinical correlation and further workup for GPA and other vasculitic conditions
  • Overlooking associated findings such as subglottic stenosis, mastoiditis, or lacrimal gland involvement that support the diagnosis of multisystem GPA rather than isolated sinusitis
Source: Reference source

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