Imaging for Suspected Rhizopus (Mucormycosis) Infection of the Nasal Passages
For initial imaging of suspected invasive fungal sinusitis including Rhizopus (mucormycosis) of the nasal passages, start with noncontrast CT maxillofacial, followed by MRI orbits, face, and neck with and without IV contrast to fully assess extrasinonasal extension. 1
Initial Imaging Strategy
CT Maxillofacial Without Contrast (First-Line)
Noncontrast CT maxillofacial is the appropriate initial imaging modality because it effectively demonstrates:
- Hyperattenuation within the involved sinuses (suggesting fungal elements, though nonspecific) 1
- Bony erosions and bone dehiscence (high specificity but limited sensitivity in early disease) 1
- Infiltration of periantral fat, pterygopalatine fossa, nasolacrimal duct and lacrimal sac 1
- Emphysematous soft tissue in the nasal cavity (a specific sign of early invasive fungal sinusitis) 1
- Severe predominantly unilateral nasal cavity mucosal thickening (high sensitivity but low specificity) 1
A validated 7-variable CT model demonstrated 88% sensitivity and 100% specificity when any 2 of the following are present: infiltration of periantral fat, pterygopalatine fossa, nasolacrimal duct/lacrimal sac, bone dehiscence, septal ulceration, and orbital involvement 1
CT also enables surgical planning with detailed sinonasal anatomy and compatibility with surgical image-guidance systems 1
MRI Orbits, Face, and Neck With and Without IV Contrast (Essential Follow-Up)
MRI with contrast must follow CT because it provides superior assessment of:
- Extrasinonasal soft tissue invasion with 85-86% sensitivity compared to CT's 57-69% 1
- The "black turbinate sign" (lack of nasal turbinate enhancement correlating with necrosis from angioinvasive disease) 1
- Orbital extension (present in 65% of cases in one study) 1
- Intracranial complications including cavernous sinus thrombosis, vascular complications, and brain involvement 1, 2
- Lack of contrast enhancement (seen in 48% of patients and a prognostic factor for disease-specific mortality) 1
In one study, extrasinonasal extension was demonstrated in all cases on MRI, making it critical for complete disease assessment 1
Combined pre- and postcontrast MRI imaging provides the best opportunity to identify and characterize potential orbital, intracranial, and vascular complications 1
Clinical Context and Pitfalls
High-Risk Population Recognition
Suspect mucormycosis in immunocompromised patients including those with:
- Neutropenia or hematologic malignancies 1
- Poorly controlled diabetes 1, 2
- Organ transplantation or immunosuppressive therapy 1
- Recent COVID-19 infection (particularly in diabetics) 2, 3
The mortality rate is 50-80%, making rapid diagnosis critical 1
Important Caveats
- CT has limited sensitivity in early disease - bone erosion and periantral fat infiltration have high specificity but limited sensitivity early on 1
- MRI has a critical limitation: T2 signal void from fungal concretions can be confused for pneumatized sinus, limiting evaluation of intrasinus disease 1
- CT and MRI are complementary, not alternatives - CT shows bone detail and surgical anatomy while MRI demonstrates soft tissue invasion and complications 1, 2
- Inflammatory tissue infiltration into infratemporal fossa, pterygopalatine fossa, or orbit without bony destruction should raise suspicion for mucormycosis 4
Advanced Imaging (Not Initial)
The following are not appropriate for initial evaluation but may be used later:
- CTA or MRA head: for vascular complications (pseudoaneurysm, thrombosis, dissection) after initial diagnosis 1
- Catheter angiography: for confirmation and treatment planning of vascular complications 1
- MRI head with contrast: complementary to assess intracranial spread beyond the field of view of MRI orbits/face/neck 1
Plain radiography, cone beam CT, PET/CT, and SPECT have no role in evaluating suspected invasive fungal sinusitis 1