Mucous retention cysts

Retention cysts of paranasal sinuses are benign lesions usually discovered incidentally on a plain sinus radiograph or cross-sectional imaging of the head. They do not usually cause symptoms.

Terminology

They are also referred to as mucous retention cysts.

Epidemiology

It is difficult to estimate their true incidence since most studies report findings of retention cysts on imaging performed for unrelated symptoms. However, an incidence of 29 -31% has been reported in studies on adults undergoing brain MRI .

Clinical presentation

Although usually discovered incidentally and asymptomatic, retention cysts can cause a headache, peri-orbital pain and nasal obstruction. They may occasionally present with repeated episodes of sinusitis.

Pathology

Retention cysts represent obstructed submucosal mucinous glands within the paranasal sinus .

Radiographic features

Retention cysts are seen on imaging as rounded dome-shaped lesions often situated on the maxillary sinus floor. They are slow growing lesions, but mucosal and cortical integrity is preserved.

Plain radiograph

Radiopaque dome-shaped lesion with a rounded edge, often seen on the floor of the maxillary sinus.

CT

Low attenuation well-defined rounded lesion within the paranasal sinus. Unless extremely large, the affected paranasal sinus usually remains aerated.

MRI

• T1: variable, often intermediate to hypointense depending on the protein content
• T2: hyperintense

Treatment and prognosis

Mostly no treatment is indicated, because of their high spontaneous regression rate . If symptomatic or causing nasal obstruction they can be surgically resected endoscopically.

Differential diagnosis

• sinonasal polyp: may be indistinguishable on CT and MRI, but mucosal retention cyst do not extend to the nasal cavity
• paranasal sinus mucocele: air within the affected paranasal sinus rules out a mucocele