Should fungal sinusitis be considered the first differential diagnosis and empirical antifungals started in a patient with bony erosion on HRCT PNS?

Bony Erosion on HRCT: Differential Diagnosis and Management

Fungal sinusitis should NOT be the automatic first differential diagnosis based solely on bony erosion, and empirical antifungals should NOT be started without tissue diagnosis. While fungal disease is an important consideration, bony erosion in sinonasal disease has multiple etiologies that require histopathological confirmation before treatment.

Critical Differential Diagnoses for Bony Erosion

Your imaging shows bilateral disease with cribriform plate and maxillary sinus wall erosion—this pattern demands consideration of several entities:

Malignancy (7-18% of isolated sinus opacification)

• Isolated maxillary or sphenoid sinus opacification carries an 18% risk of neoplasia and 7-10% risk of malignancy 1
• Squamous cell carcinoma is the most common sinonasal malignancy, with other possibilities including sinonasal undifferentiated carcinoma, adenocarcinoma, and lymphoma 1
• The bilateral cribriform plate erosion in your case is particularly concerning and mandates tissue diagnosis 1

Allergic Fungal Rhinosinusitis (AFRS)

• Approximately 20% of AFRS cases demonstrate bony erosion, but this is a non-invasive process despite the erosive appearance 1, 2
• AFRS typically presents in younger atopic patients with characteristic "peanut-butter-like" eosinophilic mucin 1
• CT shows hyperdensities (not true calcifications) from metal concentration by fungal organisms 1
• Bone erosion in AFRS occurs from pressure expansion, NOT from invasion—there is no fungal invasion into mucosa, vessels, or bone on histology 1, 3

Fungal Ball (Mycetoma)

• Typically affects a single sinus (most commonly maxillary or sphenoid), making this less likely given your bilateral disease 1
• Hyperdensities/calcifications seen in 52-77% of cases 1
• Bone erosion can occur but represents chronic pressure changes, not invasion 1

Invasive Fungal Sinusitis

• Occurs almost exclusively in immunocompromised patients (diabetes, immunosuppression, neutropenia) 1, 4
• Shows lack of mucosal enhancement ("black turbinate sign") on MRI, indicating tissue necrosis from angioinvasion 1
• Requires urgent combined surgical and medical management with systemic antifungals 5, 4

Diagnostic Algorithm

Step 1: Assess Patient Immune Status

• If immunocompromised: Consider invasive fungal sinusitis as a medical emergency requiring urgent MRI with contrast and immediate ENT consultation 1, 5, 4
• If immunocompetent: Proceed with systematic evaluation for non-invasive etiologies 1

Step 2: Obtain MRI with Contrast

• MRI is essential to differentiate inflammatory disease, fungal infection, and neoplasia 5
• MRI provides superior evaluation of soft tissue invasion, orbital involvement, and intracranial extension compared to CT alone 1
• Look for lack of enhancement (suggests invasive fungal disease) versus enhancement patterns suggesting tumor 1
• The bilateral cribriform plate erosion in your case necessitates evaluation for intracranial extension 1

Step 3: Obtain Tissue Diagnosis

• Biopsy is mandatory before initiating any specific therapy 1, 5
• Endoscopic examination with tissue sampling for histopathology and fungal culture is the gold standard 5
• Histology will distinguish between: non-invasive fungal disease (AFRS or fungal ball), invasive fungal disease, and malignancy 1, 6

Why Empirical Antifungals Should NOT Be Started

For Non-Invasive Fungal Disease (AFRS and Fungal Ball)

• Surgery is the primary and definitive treatment—antifungal medications play NO role 1, 5, 3
• AFRS requires endoscopic debridement with removal of eosinophilic mucin and polyps, followed by topical steroids 1, 3
• Fungal ball requires simple endoscopic sphenoidotomy with complete removal of fungal debris, with recurrence rates of only 3-4% with adequate surgical removal 5
• Even with extensive bone erosion and cranial neuropathy, endoscopic surgical debridement without systemic antifungals leads to resolution 3

For Invasive Fungal Disease

• Requires combined aggressive surgical debridement AND systemic antifungals (voriconazole for Aspergillus, amphotericin B for mucormycosis) 5, 4, 6
• However, this diagnosis requires histologic demonstration of fungal invasion into mucosa, submucosa, bone, or vessels 6
• Starting antifungals empirically without confirming invasion may delay appropriate surgical management 6

For Malignancy

• Antifungals would be inappropriate and delay definitive oncologic treatment 1

Clinical Pitfalls to Avoid

• Do not assume bone erosion equals invasive disease: AFRS causes bone erosion in 20% of cases through expansion, not invasion 1, 2
• Do not mistake AFRS for malignancy: Both can present with bone erosion and mass effect, requiring biopsy for differentiation 3, 7
• Do not use antifungals for non-invasive fungal disease: This represents inappropriate therapy and may cause drug toxicity without benefit 1, 5, 3
• Do not delay tissue diagnosis: The 7-18% malignancy risk with isolated sinus opacification and bone erosion mandates early surgical intervention for diagnosis 1

Recommended Management Pathway

Immediate next steps for your patient:

1. Obtain MRI with contrast to evaluate for soft tissue invasion, intracranial extension, and enhancement patterns 1, 5
2. Arrange urgent ENT consultation for endoscopic evaluation and biopsy 5
3. Assess immune status (diabetes, HIV, immunosuppressive medications, neutrophil count) 4, 6
4. Do NOT start empirical antifungals until tissue diagnosis is established 1, 5, 6

The definitive diagnosis and appropriate treatment pathway can only be determined after histopathological examination confirms whether this represents non-invasive fungal disease, invasive fungal disease, or malignancy 1, 5, 6.