Coronal (a) and axial (b) CT images (soft tissue window).
Head & neck imagingCase Type
Ana Primitivo1, Sofia Amante2, Carla Moreira3, and José Maria Barros3Patient
37 years, female
37-year-old woman with a history of recurrent respiratory infections. Physical examination showed mild right proptosis. There was no history of trauma or comorbidities.
CT depicted a homogeneous substance of mucoid attenuation, close to brain parenchyma, leading to expansion of the right sinus cavities, with demineralisation involving the orbital roof and the posterior wall of the frontal sinus (Fig. 1 and 2).
On magnetic resonance imaging (MRI), a large well-defined lobulated T1-weighted image (WI) and T2 WI homogeneously hyperintense cystic lesion was seen arising from the right frontal and ethmoidal sinus (Fig. 3).
Bulging of extraconal structures was seen along the superior and medial aspect of the right orbit with associated mild proptosis. (Fig. 4) The lesion did not show intraconal extension and the intraocular muscles were just slightly molded. Thinning and bulging of the frontal bone cortex, without extension to the anterior cerebral fossa or disruption of the dura was noted (Fig. 2). A thin rim of enhancement was seen on contrast administration (Fig. 3).
Paranasal sinus mucoceles are benign, expansile cystic masses, resulting from accumulation and retention of mucus secretion in cases where the sinus drainage is obstructed. [1, 2]
On histopathology they are cyst-like structures lined with respiratory epithelium single-layered, pseudostratified, ciliated, columnar epithelium, filled with mucus. 
It may be due to previous trauma, surgery, nasal polyposis, tumours or chronic inflammation.
The clinical presentation is variable, usually with insidious symptoms, and low potential to cause morbidity. Symptoms are generally due to compression of neighbouring structures, with headache, nasal obstruction and ophthalmological alterations. 
A mucopyocele occurs when a mucocele becomes infected, and may course with sinusitis or orbital cellulitis.
Pressure is generated in the obstructed sinus by continued mucous secretion resulting in gradual thinning, distention and erosion of one or more of its walls. Prostaglandins and collagenases aid in osteolysis and further enhance the expansion. [5, 6]
Its incidence is higher between the third and fourth decades of life, with no predominance of sex. [4, 7, 8]
Most frequent locations are the frontal sinuses (60-65%), ethmoid (20-25%), maxillary (10%) and sphenoid sinuses (1% to 2%). 
CT offers detailed information on the bone structure, such as the presence of bone erosions, adding important preoperative information. The mucocele content has mucoid attenuation, close to the attenuation of brain parenchyma. [8, 9] MRI is superior in identifying the relationship with the neighbouring structures. The radiological appearance varies along the time. Initially, it will show a predominantly fluid content, so the corresponding image will be hypointense on T1-WI, and hyperintense on T2-WI. Over time, the protein contents may increase, resulting in hyperintense images both on T1- and T2-WI. Gadolinium enhanced MRI scans should always be performed, since there is a significant overlap in signal intensities of mucoceles, tumours and obstructed sinuses on unenhanced MR scan. Mucoceles should strictly be devoid of enhancement, with the exception of a regular linear peripheral enhancement. Enhancement within the centre of the lesion or even nodular peripheral enhancement should raise the possibility of a coexisting tumour. [4, 9, 10]
The endonasal surgery is the mainstay of today’s management of mucoceles. The main goal is the complete removal of both the lesion and the sinusal mucosa, thus preventing disease recurrence. 
Surgery with transnasal access route was performed since there wasn’t an obvious intracranial extension (Fig. 5-7). [11-13]
Although there is a low recurrence rate (<10%), a long follow up is generally recommended. [6, 7, 14]
Written informed patient consent for publication has been obtained.
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