Sphenoid sinus mucocele

Findings

CT: Expansion of the sphenoid sinus by a soft-issue density. The clivus appears eroded.
MRI: Expanded sphenoid sinus. Homogeneous material is present within the sinus cavity which is both T1 bright and T2 bright. Mass effect is present on both cavernous sinuses. The sellar contents appear normal. There is no evidence of enhancement with gadolinium.


Diagnosis: Sphenoid sinus mucocele


Mucocele is the most common lesion to cause expansion of the paranasal sinuses and results from the accumulation of mucoid secretions within an obstructed sinus or an obstructed chamber within a septated sinus. Both mucoceles and mucous retention cysts are formed by cuboidal epithelium surrounding mucoid secretions. Mucoceles fill a sinus cavity when the draining sinus ostia are blocked, usually by inflammatory changes or a tumor.

Mucoceles are more common in adults and usually a history of prior sinusitis or sinus polyposis can be obtained. Mucoceles are more common in individuals with cystic fibrosis. Classic mucoceles are non-infected and present with complaints resulting from the mass effects such as proptosis, frontal bossing, inability to breathe through the nose, orbital mass (frontal or ethmoidal), medial gaze abnormality (ethmoid), or a change in voice pitch. Pain is unusual and implies super infection. The most commonly involved sinuses are the frontal (60%) > ethmoid (30%) > maxillary (10%) > sphenoid (1%). Sphenoid sinus mucoceles have the highest rate of surgical complications (blindness) reflecting their proximity to the optic nerves. Sphenoid mucoceles usually expand antero-laterally into the ethmoid sinuses and orbital apices. Expansion may also occur into the sella, the cavernous sinuses, into the nasopharynx, or intra-cranially (rarely).


Diagnosis

Sinus expansion can occur with mucoceles or neoplasms. The CT appearance of a soft tissue mass can be similar to mucocele. Sinusitis does not expand the sinus cavity. Surrounding bony sclerosis suggests infection. Calcifications may be present with superimposed fungal infections.


Therapy

Surgical drainage (transsphenoidal marsupialization into an adjacent sinus cavity).


Radiology

Plain film: The sinus may appear clouded, and the normal scalloped contour is lost as the mass enlarges. The normal white mucoperiosteal line is poorly seen. If preceded by chronic sinusitis, the sinus bones may show reactive bony changes.
CT: Mucocele usually appears as an expanded sinus cavity filled with material of homogeneous mucoid attenuation (10-0 HU). Rarely the material is of higher attenuation thought due to a higher protein content. Mucoceles generally do not enhance.
MRI: Signal is dominated initially by water content (95%). With chronicity (several months) the protein concentration and viscosity of the fluid increase and so does the T1WI signal. Usually T2WI bright; may decrease with time and lower water content.