What are the typical CT findings in fungal ball sinusitis?

CT Findings in Fungal Ball Sinusitis

The most diagnostic CT findings in fungal ball sinusitis are hyperattenuation/calcifications within the sinus and erosion of the inner wall of the sinus. 1, 2

Characteristic CT Findings

Primary Diagnostic Features

• Hyperattenuation/Calcifications: Present in 52-77% of cases, these represent trace metal elements in the fungus rather than true calcifications 1
• Erosion of the inner wall of the sinus: Highly specific finding that helps differentiate fungal ball from other conditions 1, 2
• Sinus opacification: Usually unilateral and complete 1

Secondary Diagnostic Features

• Sclerosis/neo-osteogenesis of the sinus wall: Common in fungal ball compared to normal patients 1, 2
• Heterogeneous opacification of the affected sinus 2
• Absence of air-fluid levels: Helps differentiate from bacterial sinusitis 2
• Smaller sinus volume on the affected side compared to the contralateral normal side 1

Anatomical Distribution

• Maxillary sinus: Most commonly affected (84.4% of cases) 3
• Sphenoid sinus: Second most common location (14.4% of cases) 3
• Ethmoid sinus: Rarely affected (0.6% of cases) 3
• Multiple sinus involvement: Uncommon in fungal ball, which typically affects a single sinus 4

Differential Diagnostic Features

Fungal ball can be differentiated from other conditions by these imaging characteristics:

• Allergic Fungal Sinusitis: Shows sinus expansion, extensive bone erosion, multiple sinus involvement, and heterogeneous opacities 4
• Invasive Fungal Sinusitis: Demonstrates homogeneous opacity (isodense or hyperdense to muscle), homogeneous contrast enhancement, and extra-sinus extension greater than intra-sinus component 4
• Bacterial Sinusitis: Typically shows mucosal thickening, air-fluid levels, and lacks calcifications 1
• Sinonasal Neoplasia: May mimic fungal ball but usually shows more aggressive bone destruction and enhancement patterns 1

MRI Findings

When MRI is performed, fungal ball typically shows:

• T1-weighted images: Iso- or hypointense signal (64.7% of cases) 1, 5
• T2-weighted images: Marked hypointensity (88.2% of cases) 1, 5
• T2 signal void from fungal concretions can be confused for a pneumatized sinus 1

Clinical Pearls and Pitfalls

• Diagnostic Accuracy: Calcifications and erosion of the inner wall of the sinus are the two most significant CT features that increase diagnostic accuracy for fungal ball 2
• Cone Beam CT Limitation: Hyperdensities are less commonly seen on cone beam CT compared to conventional CT 1
• Diagnostic Caution: Isolated maxillary or sphenoid sinus opacification can also indicate neoplasia (18%) or malignancy (7-10%), so early surgical intervention should be considered 1
• Dental Association: Consider dental evaluation in maxillary sinus fungal ball cases, as there may be an association with endodontic treatment 1
• Contrast Enhancement: On contrast-enhanced CT, the fungal ball typically appears hyperattenuating in the central area with peripheral mucosal thickening that enhances 5

By recognizing these characteristic imaging findings, clinicians can accurately diagnose fungal ball sinusitis preoperatively and plan appropriate surgical intervention, which is the primary treatment for this condition 1, 3.