Paranasal sinus mucocele

• Complete opacification of an entire sinus with bony expansion and cortical thinning on CT
• Peripheral or absent contrast enhancement distinguishing mucoceles from enhancing malignancies
• Variable MRI signal intensity (low T1/high T2 for water-rich or high T1/low T2 for protein-rich content) without internal enhancement
• Mass effect on adjacent structures such as orbital displacement, proptosis, or orbital floor elevation

• CT demonstrates complete sinus opacification with expanded margins that are typically thin-walled, occasionally with complete bone resorption and bony defects allowing extension into adjacent tissues.
• Peripheral calcification may be present within the sinus walls on CT.
• CT shows variable attenuation of sinus contents ranging from near-water density to hyperattenuating thick desiccated secretions depending on hydration and protein concentration.
• MRI T1 signal is typically low (water-rich content most common) but may be high if protein-rich; T2 signal is typically high (water-rich most common) but may be low with protein-rich content.
• Post-gadolinium MRI shows peripheral enhancement only if present, with no internal enhancement; enhancement is absent in uncomplicated mucoceles.
• Frontal sinus is involved in approximately two-thirds of mucoceles, followed by ethmoidal sinuses (~25%); maxillary and sphenoid involvement is less common.
• Fungal colonization can produce very low signal on both T1 and T2 sequences, potentially mimicking aerated normal sinus, particularly with Aspergillus.
• CT is essential for assessing bony changes and detecting defects; MRI is superior for evaluating orbital and intracranial extension, mass effect on adjacent structures, and soft tissue involvement.

• Paranasal sinus tumor (inverted papilloma, sinonasal carcinoma): distinguished by internal heterogeneous enhancement and more aggressive bone destruction rather than thinning and expansion.
• Acute sinusitis: lacks the characteristic bony expansion and cortical thinning; shows mucosal rather than complete sinus thickening.
• Mucus retention cyst: does not completely fill the sinus cavity and lacks bony expansion of the sinus walls.
• Antrochoanal polyp: focally protrudes through the ostiomeatal complex rather than completely filling and expanding a single sinus.
• Fungal mycetoma: demonstrates sclerosis of bony walls rather than thinning; lacks sinus expansion.
• Aspergillus infection: may show low T1 and T2 signal similar to mucoceles but typically lacks the degree of sinus expansion and bony thinning seen in true mucoceles.

Describe mucoceles as complete opacification of the [specify sinus location] with thinned and expanded bony margins, peripheral or absent enhancement, and assess for mass effect on adjacent structures (orbit, brainstem, pituitary) and any bony dehiscence indicating risk for intracranial or orbital extension; note whether imaging findings are consistent with infection (pyocele) based on clinical context.

• Fungal colonization of mucoceles can produce very low T1 and T2 signal mimicking normal aerated sinus, potentially leading to diagnostic error if MRI is misinterpreted without correlation to CT.
• Failure to recognize that mucoceles enhance only peripherally, not throughout; diffuse internal enhancement should raise suspicion for malignancy.
• Missing mass effect on adjacent critical structures (orbit, brainstem, pituitary) by focusing only on the sinus itself rather than assessing regional anatomy and potential complications.
• Overlooking bony defects and sites of bone resorption that indicate risk for extension into orbit, intracranial space, or subcutaneous tissues, which may alter surgical approach and urgency of treatment.