Splenic simple cyst (epidermoid cyst) is a true cyst with epithelial lining. It is of congenital origin and lined by squamous or cuboidal epithelium. Contents are clear serous fluid, comprising 10-20% of all true splenic cysts (pseudocysts account for 80%). Usually asymptomatic and discovered incidentally. Large cysts (>5 cm) may present with left upper quadrant pain, early satiety, or complications (hemorrhage, infection, rupture). On imaging, it appears as a water-density, thin-walled, non-enhancing, unilocular cystic lesion. Wall calcification is seen in 10-15% of cases and helps differentiate from pseudocyst (calcification is more common in pseudocyst). No risk of malignant transformation, but partial splenectomy or unroofing may be considered for symptomatic lesions.
Age Range
10-70
Peak Age
35
Gender
Equal
Prevalence
Common
Splenic simple cyst is a congenital lesion developing from mesothelial or endodermal cell remnants entrapped in the splenic parenchyma during embryonic development. The epithelial lining may be squamous, cuboidal, or transitional — this histological diversity supports different embryonic origin theories. Intracystic fluid accumulates through epithelial cell secretion and is clear, serous in character. Water density (0-20 HU) on CT reflects the low protein concentration and homogeneous water composition of intracystic fluid — iodinated contrast agent cannot penetrate the cyst as the wall is non-vascular with an endothelial barrier. Marked hyperintensity on T2-weighted MRI results from the very long T2 relaxation time of free water. Hypointensity on T1 results from the long T1 value of water. Anechoic appearance on US results from the homogeneity of intracystic fluid and absence of internal interfaces to reflect ultrasound waves. Posterior acoustic enhancement results from minimal absorption of ultrasound energy by fluid. Over time, dystrophic calcification may develop in the cyst wall — a result of chronic mechanical stress and epithelial turnover.
Anechoic cystic lesion with posterior acoustic enhancement and thin wall on US + non-enhancing water-density lesion on CT is diagnostic for simple cyst. Absence of enhancement (differentiation from solid component) and high ADC (differentiation from abscess) confirm diagnosis.
In the portal venous phase, a water-density (0-20 HU), thin smooth-walled, non-enhancing, well-defined round or oval cystic lesion is seen. Content is homogeneous without debris or solid components. Wall does not enhance. Sharp boundary exists between the lesion and splenic parenchyma. Calcification may be seen along the wall in 10-15% of cases as thin curvilinear or punctate pattern.
Report Sentence
A water-density, thin-walled, non-enhancing, well-defined cystic lesion is seen in the spleen, consistent with a simple cyst.
Markedly homogeneous hyperintensity equal to CSF on T2-weighted MRI. Surrounded by thin smooth hypointense wall. No internal debris, septation, or solid components. Marked hyperintense signal persists on T2 STIR. T2 hyperintensity is similar to hemangioma but simple cyst shows no enhancement — this is the key differentiating point.
Report Sentence
The splenic lesion shows markedly homogeneous hyperintensity equal to CSF on T2-weighted MRI surrounded by a thin hypointense wall; consistent with a simple cyst.
On T1-weighted MRI, the cyst shows markedly hypointense signal relative to splenic parenchyma. Homogeneous low signal reflects the long T1 relaxation time of free water. T1 signal increase may be seen with proteinaceous or hemorrhagic content — complicated cyst should be considered in this case. Wall and content do not enhance on post-contrast T1 series.
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The cystic lesion in the spleen shows markedly hypointense signal on T1-weighted MRI with no enhancement on post-contrast series.
On B-mode US, a well-defined, round or oval, anechoic (no internal echoes) cystic lesion is seen. Thin smooth hyperechoic wall surrounds it. Posterior acoustic enhancement is prominent — tissues behind the cyst appear brighter. No internal septation, debris, or solid components. No vascularity detected in cyst wall or content on Doppler US. Size varies — can range from 1 cm to 20+ cm.
Report Sentence
A well-defined, anechoic, thin-walled cystic lesion is seen in the spleen with prominent posterior acoustic enhancement; consistent with a simple cyst.
On unenhanced CT, a water-density (0-20 HU), well-defined, homogeneously hypodense cystic lesion is seen. Density value is significantly lower than splenic parenchyma (40-60 HU). Wall calcification is visible as thin curvilinear or punctate hyperdensity in 10-15% of cases. Unenhanced CT alone may be insufficient to differentiate simple cyst from pseudocyst or complicated cyst — contrast-enhanced phase is needed to evaluate wall enhancement.
Report Sentence
A water-density (8 HU), well-defined cystic lesion is seen in the spleen on unenhanced CT.
On DWI, simple cyst shows no diffusion restriction — signal loss at high b-value (T2 shine-through may occur but confirmed by high ADC values on ADC map). ADC value is very high (>2.5 × 10⁻³ mm²/s) because free water molecules move without restriction. This feature is critical in differentiating simple cyst from abscess (abscess shows low ADC — viscous pus restricts diffusion) and solid tumors.
Report Sentence
No diffusion restriction is seen in the cystic lesion on DWI with high ADC values; this finding is consistent with simple cyst and excludes abscess.
Criteria
Squamous epithelial lining. Most common true splenic cyst type. May contain keratohyalin granules and keratinized debris.
Distinct Features
Usually unilocular, clear fluid. Calcification rare. No malignant potential.
Criteria
Mesothelial cell lining. Develops from peritoneal mesothelial remnants.
Distinct Features
May be multilocular. May contain thin septa (different from simple cyst). Calretinin (+) immunohistochemistry.
Criteria
Contains ectoderm, mesoderm, and endoderm elements. Extremely rare in spleen.
Distinct Features
Mature tissue elements in content (fat, hair, teeth). Fat signal and chemical shift artifact on MRI.
Distinguishing Feature
Pseudocyst is associated with trauma/infarct history, wall may be thick and irregular, calcification more common (25-50%) and coarser ('eggshell'). Content may be above water density (20-40 HU) due to protein/debris.
Distinguishing Feature
Abscess shows marked diffusion restriction on DWI (low ADC — viscous pus); simple cyst shows no restriction (high ADC). Abscess may have thick, irregular enhancing rim and internal gas.
Distinguishing Feature
Lymphangioma shows multilocular cystic structure with thin septa and subcapsular growth pattern; simple cyst is unilocular without septa.
Distinguishing Feature
Hemangioma shows progressive peripheral nodular enhancement with centripetal fill-in on contrast-enhanced series; simple cyst shows no enhancement in any phase.
Urgency
routineManagement
surveillanceBiopsy
Not NeededFollow-up
12-monthSplenic simple cyst is a benign lesion with no risk of malignant transformation. No treatment is needed for small, asymptomatic cysts — annual US follow-up is sufficient. For >5 cm cysts or symptomatic cases (pain, early satiety, compression), treatment options include laparoscopic unroofing (marsupialization), partial splenectomy, or percutaneous aspiration-sclerotherapy. Total splenectomy should be avoided — preservation of splenic function is important. Cyst perforation, infection, or hemorrhage may require emergency intervention. Biopsy is not needed — imaging findings are diagnostic. Hydatid cyst should be considered in differential diagnosis (especially in endemic areas) — serology (ELISA, IHA) and calcification pattern are helpful.
Splenic simple cyst is usually asymptomatic and incidentally discovered. No follow-up or treatment is needed when typical features are present. Large cysts may be symptomatic and partial splenectomy or drainage may be considered.