Mucosal retention cyst is a benign, cystic lesion resulting from obstruction of seromucinous glands in the paranasal sinus mucosa. It most commonly occurs in the maxillary sinus and is generally detected incidentally. Its prevalence is between 10-35% and most are asymptomatic. On CT, it appears as a smooth-bordered, dome-shaped, homogeneous soft tissue density lesion arising from the sinus wall. No treatment is required; however, giant retention cysts that completely fill the sinus can rarely be symptomatic.
Age Range
10-80
Peak Age
40
Gender
Equal
Prevalence
Very Common
Retention cysts form due to obstruction of the ducts of seromucinous glands in the sinus mucosa. Due to duct obstruction, gland secretions cannot drain and accumulate within the cyst lumen, with the cyst growing under progressively increasing pressure. The cyst wall is lined by glandular epithelium — this feature differs from polyps (edema-based, epithelium-lined but no gland wall). Cyst content is usually serous or mucinous fluid and appears at water-soft tissue density (10-25 HU) on CT. Cysts grow slowly and do not compress surrounding tissue; therefore bone remodeling or destruction is not expected. They are very common in the general population with a prevalence of 10-35% and are often reported as incidental CT findings. Some authors do not even recommend reporting small, smooth-bordered cysts because they have no clinical significance.
A smooth-contoured, dome-shaped, homogeneous low-density (10-25 HU) lesion arising from the sinus wall is the pathognomonic CT appearance of a retention cyst. It does not cause bone changes, does not completely fill the sinus, and does not enhance. Due to these morphologic features, no additional imaging or follow-up is required — diagnosis is definitive on CT. These lesions are found as incidental findings in 10-35% of the general population, are clinically insignificant, and reporting practice varies by institution.
On non-contrast CT, a smooth-bordered, dome-shaped, soft tissue density lesion arising from the sinus wall is seen. The lesion is homogeneous without internal septation, calcification, or irregular contour. Its density is usually between 10-25 HU reflecting serous/mucinous fluid. Size can range from a few millimeters to 3-4 cm. Those arising from the sinus floor are most common, but they can also originate from medial, lateral, or posterior walls. It does not completely fill the sinus — usually occupying less than half the sinus volume. Bony structures appear intact and of normal thickness.
Report Sentence
A smooth-bordered, dome-shaped, homogeneous soft tissue density lesion is noted at the right maxillary sinus floor, consistent with a retention cyst; assessed as an incidental finding.
On MRI T2-weighted sequences, the retention cyst shows markedly hyperintense signal — producing bright water-like signal due to serous/mucinous fluid content. The cyst shows homogeneous signal without internal septation or solid component. The cyst wall is thin and may be seen as a thin low-signal line on T2. Surrounding sinus mucosa may be normal or mildly thickened. T2 hyperintensity differentiates retention cyst from desiccated secretions (T2 hypointense) and fungal material (T2 blackout). The spherical/dome shape and homogeneous high T2 signal of the cyst are usually sufficient for diagnosis.
Report Sentence
A smooth-bordered, dome-shaped lesion showing homogeneous hyperintense signal on MRI T2-weighted sequences is noted in the left maxillary sinus, consistent with a retention cyst.
On T1-weighted sequences, the retention cyst appears at low-intermediate signal intensity. Serous cyst fluid shows near-water T1 signal (low signal); proteinaceous cyst fluid may show slightly higher T1 signal. On contrast T1, cyst content does not enhance — thin cyst wall may show mild enhancement. Non-enhancement of the cyst is important in differential diagnosis from solid lesions. As cyst size increases, T1 signal intensity may increase depending on protein concentration.
Report Sentence
The cystic lesion in the right maxillary sinus shows low signal intensity on T1-weighted sequences and does not enhance on contrast study; consistent with a retention cyst.
Retention cysts in the maxillary sinus can be evaluated by ultrasonography in certain situations. The cyst appears as an anechoic or hypoechoic, smooth-bordered, dome-shaped lesion. Posterior acoustic enhancement (through transmission) supports serous fluid content. Absence of internal echoes differentiates from solid lesions. However, the role of ultrasonography in paranasal sinus evaluation is limited and CT is the gold standard. Ultrasonography can be used for sinus pathology screening particularly in pregnant women and children.
Report Sentence
An anechoic, smooth-bordered, dome-shaped lesion is noted on right maxillary sinus ultrasonography, consistent with a retention cyst.
Retention cysts do not cause any changes in surrounding bone structures — bony walls appear of normal thickness and density. There is no bone sclerosis, remodeling, or destruction. This feature differentiates retention cysts from mucocele (bone remodeling/expansion), tumor (bone destruction), and chronic sinusitis (bone sclerosis) — pathologies that cause bone changes. The sinus ostium is usually open — sinus drainage is not obstructed. Even in giant cysts, bone changes are not expected; this reflects the low-pressure, slow-growing nature of the cyst.
Report Sentence
The cystic lesion in the left maxillary sinus does not cause any changes in surrounding bone structures, with normal bone thickness and density preserved.
Criteria
Forms from obstruction of serous glands. Contains thin, serous fluid. CT density 10-15 HU (water-like).
Distinct Features
Water-like low density on CT, markedly T2 hyperintense, T1 low signal on MRI. Usually small (<2 cm) and incidental.
Criteria
Forms from obstruction of mucinous glands. Contains thick, mucinous fluid. CT density 15-25 HU.
Distinct Features
Slightly higher density than serous cyst on CT, T2 hyperintense but slightly lower signal than serous cyst on MRI, slightly higher signal on T1 (protein content). Size may be larger than serous cyst.
Criteria
Retention cyst filling >75% of sinus volume. Rare and may be symptomatic (facial pressure, nasal obstruction). Surgery (marsupialization) may be considered.
Distinct Features
Smooth-bordered cystic lesion nearly completely filling the sinus on CT. May be confused with mucocele but no bone remodeling/expansion (mucocele expands bone). Clinical correlation required.
Distinguishing Feature
Mucocele completely fills the sinus AND expands sinus walls (bone remodeling); retention cyst does not completely fill the sinus and does not cause bone changes. Mucocele usually in frontal or ethmoid sinus; retention cyst usually in maxillary sinus.
Distinguishing Feature
Polypoid mucosal changes may have irregular contours, be multiple and bilateral; retention cyst is single, smooth-bordered, and dome-shaped. Polyps are usually seen with OMC obstruction while retention cyst is an isolated lesion.
Distinguishing Feature
Acute sinusitis shows diffuse mucosal thickening and air-fluid level; retention cyst is a focal, dome-shaped lesion without air-fluid level. Acute sinusitis is symptomatic while retention cyst is usually asymptomatic.
Urgency
surveillanceManagement
conservativeBiopsy
Not NeededFollow-up
Takip gerekmez. Tedavi gerekmez. İnsidental bulgu olarak raporlanır (bazı kurumlar küçük kistlerin raporlanmasını bile önermez). Dev kistlerde semptomatik ise marsupializasyon düşünülebilir.Mucosal retention cysts are clinically insignificant incidental findings. No treatment is required and follow-up is not recommended. In rare cases, giant cysts that completely fill the sinus may cause facial pressure or nasal obstruction — endoscopic marsupialization can be performed in this situation. Retention cysts have no risk of malignant transformation. In reporting, it is recommended to note as 'incidental finding of no clinical significance' to avoid unnecessary anxiety. Retention cysts are frequently seen on CTs obtained for sinusitis investigation independently from sinusitis and do not affect the sinusitis diagnosis.
Retention cysts are usually incidental findings and require no treatment. If symptomatic or enlarging to obstruct sinus drainage, they can be removed by FESS. There is no risk of malignant transformation.