Adrenal pseudocyst is a cystic lesion lacking a true epithelial lining, typically developing from organization of prior adrenal hemorrhage, infection, or vascular event. It comprises approximately 40% of all adrenal cysts and is the most common subtype. Unlike simple (endothelial) cysts, it demonstrates a thick fibrous wall, variable amount of wall calcification, and proteinaceous/hemorrhagic internal content. Internal density on CT may exceed water density (20-50 HU) due to hemorrhagic or proteinaceous fluid. It is frequently detected incidentally and is usually asymptomatic; large lesions may cause abdominal pain or mass effect symptoms. There is a slight female predominance. While benign, it must be differentiated from cystic adrenocortical carcinoma and cystic degeneration of pheochromocytoma. Treatment involves follow-up for small asymptomatic lesions and surgery or percutaneous drainage for large or symptomatic lesions.
Age Range
30-70
Peak Age
50
Gender
Female predominant
Prevalence
Rare
Adrenal pseudocyst develops from organization of hemorrhage, infection, or vascular event within the adrenal gland over time. The most common cause is adrenal hemorrhage, which may be spontaneous (anticoagulant use, coagulopathy, stress, sepsis) or traumatic. After hemorrhage, lysis of blood cells and fibrinolytic processes begin; a fibrous tissue capsule develops around the organizing hematoma, but no true epithelial lining (endothelial or epithelial cell layer present in simple cysts) forms — hence the term 'pseudo' cyst. Dystrophic calcification may develop within the fibrous wall over time; this calcification mechanism is based on calcium-phosphate precipitation in necrotic tissue, and wall calcification (eggshell or coarse calcification) is a distinguishing feature of pseudocyst. High internal density on CT (>20 HU) results from proteinaceous or hemorrhagic fluid content — protein molecules and hemoglobin degradation products increase X-ray attenuation more than water (0 HU). T1 hyperintensity on MRI results from the T1-shortening effect of methemoglobin (subacute hemorrhage) or proteinaceous fluid; paramagnetic methemoglobin accelerates T1 relaxation of surrounding water protons through dipole-dipole interaction. T2 signal varies depending on content composition — fluid component is hyperintense, hemosiderin deposition shows hypointense signal.
A cystic adrenal lesion with thick fibrous wall calcification (eggshell or coarse pattern) combined with internal density above water (>20 HU) is the most characteristic finding for pseudocyst originating from organized hemorrhage and is pathognomonic for differentiation from simple adrenal cyst.
Well-circumscribed, thick fibrous-walled cystic adrenal lesion on non-contrast CT. Internal density is 20-50 HU, higher than water density (0-10 HU) of simple cysts. Wall calcification is present in 40-60% of cases; calcification pattern may be thin peripheral eggshell or irregular coarse. Fluid-fluid level may be seen in internal content (settled blood products). Lesion size varies widely (2-30 cm), average 8-10 cm.
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Thick-walled cystic lesion with wall calcification in the adrenal gland, with internal density above water density (approximately ... HU), consistent with proteinaceous/hemorrhagic content and pseudocyst.
On contrast-enhanced CT, the fibrous wall shows mild to moderate enhancement while no enhancement is seen in the internal fluid content. This pattern confirms the benign, avascular internal structure of the pseudocyst. Wall enhancement should be smooth and uniform; irregular, nodular, or thick wall enhancement should raise suspicion for a solid tumor with cystic degeneration (pheochromocytoma, adrenocortical carcinoma). Presence of mural nodule questions the pseudocyst diagnosis and requires further evaluation (MRI, biopsy).
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The fibrous wall of the cystic lesion shows mild enhancement but no enhancement is observed in the internal fluid content; no mural nodule is detected, and this pattern is consistent with adrenal pseudocyst.
Internal content shows hyperintense signal on T1-weighted images — this reflects the presence of methemoglobin (subacute hemorrhage) or proteinaceous fluid in hemorrhagic-origin pseudocysts. Signal intensity may be homogeneous or heterogeneous; fluid-fluid level may also be visible on T1. The fibrous wall appears hypointense on T1. Wall enhancement without internal enhancement on contrast-enhanced T1. This T1 hyperintensity pattern differs from simple cyst (T1 hypointense, T2 hyperintense) and suggests hemorrhagic/proteinaceous origin.
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Internal content of the cystic lesion shows hyperintense signal on T1-weighted images, consistent with hemorrhagic or proteinaceous fluid; simple cyst is excluded and pseudocyst is the leading diagnosis.
Variable signal of internal content on T2-weighted images. Fluid component shows high T2 signal (hyperintense), while hemosiderin deposits and organized blood products create low-signal (hypointense) foci. Fluid-fluid level can be clearly seen on T2 — clear fluid above (hyperintense), settled blood products below (hypointense). Fibrous wall appears markedly hypointense on T2 (collagen). Wall calcification appears as signal void on T2.
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Fluid-fluid level observed in the internal content of the cystic lesion on T2-weighted images with hypointense signal in the lower layer due to hemosiderin/blood products; the fibrous wall is hypointense, and these findings are consistent with hemorrhagic pseudocyst.
No significant diffusion restriction in cyst content on DWI — signal drop at high b-values and high signal on ADC map. This finding confirms that the cyst content consists of acellular fluid. Absence of diffusion restriction is important for differentiation from abscess cavity (viscous content showing diffusion restriction in purulent fluid). Focal diffusion restriction along the wall should suggest presence of mural nodule or solid component.
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No diffusion restriction in the cystic lesion content, excluding abscess and consistent with benign cystic lesion with acellular fluid content (pseudocyst).
No enhancement in internal fluid content on delayed phase (5-15 minute) CT. This delayed phase finding is important because some solid tumors (especially fibrosis-prone tumors like cholangiocarcinoma) can show delayed enhancement. Absence of delayed internal enhancement confirms the true cystic (avascular) nature of the lesion. Wall enhancement may persist or mildly increase on delayed phase (slow contrast accumulation in fibrous tissue).
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No enhancement in cyst content on delayed phase, confirming avascular cystic structure (pseudocyst); no solid component or mural nodule is detected.
Criteria
Cystic lesion organizing after adrenal hemorrhage; may have history of anticoagulant use, trauma, or spontaneous bleeding
Distinct Features
Most common type; T1 hyperintense hemorrhagic content, fluid-fluid level, hemosiderin deposition; wall calcification develops over time; clinical history may include bleeding risk factors
Criteria
Cystic lesion developing after adrenal infection (tuberculosis, fungal infection, HIV-related)
Distinct Features
Thicker and more irregular wall; coarse calcifications more frequent; more heterogeneous internal content (caseous necrosis remnants); bilateral involvement possible in tuberculosis; clinical history with infection findings
Criteria
Pseudocyst exceeding 10 cm in size; may compress adjacent structures
Distinct Features
Displacement of kidney, spleen, or liver may be seen; differentiation from organ of origin may become difficult (adrenal vs retroperitoneal); higher likelihood of being symptomatic; surgical resection generally required; histopathological examination after surgery mandatory for malignant cystic tumor exclusion
Distinguishing Feature
Simple cyst is thin-walled, water density (0-10 HU), no calcification, T1 hypointense; pseudocyst is thick-walled, >20 HU density, wall calcification, and T1 hyperintense content
Distinguishing Feature
Acute/subacute adrenal hemorrhage is an unorganized hemorrhagic collection without distinct capsule/wall formation; MRI signal changes over time (acute→subacute→chronic); pseudocyst is organized, encapsulated, chronic lesion; hemorrhage shrinks with follow-up while pseudocyst remains stable or grows very slowly
Distinguishing Feature
Cystic degeneration of pheochromocytoma contains solid components and enhancing mural nodules; markedly hyperintense solid areas on T2; MIBG positive; catecholamines elevated; pseudocyst has no solid component/mural nodule, MIBG negative, catecholamines normal
Distinguishing Feature
Cystic adrenocortical carcinoma has irregular thick wall, enhancing solid components/mural nodules, invasive margins; frequently hormonally active; pseudocyst has smooth wall, no solid component, non-invasive and non-functional; mural nodule evaluation on contrast-enhanced CT is critical for differentiation
Urgency
routineManagement
surveillanceBiopsy
Not NeededFollow-up
12-monthAdrenal pseudocyst is a benign lesion and conservative follow-up is sufficient in most cases. Size and morphology surveillance with CT or MRI at 6-12 month intervals is recommended for small (<4 cm) asymptomatic lesions. Surgical resection (adrenalectomy) or percutaneous aspiration/drainage may be performed for large (>6 cm) or symptomatic lesions. Biochemical evaluation should be performed in all cases — catecholamines (pheochromocytoma exclusion) and cortisol (functional adenoma exclusion). Surgical resection and histopathological examination is mandatory when mural nodule, irregular wall thickening, or solid component is present due to malignancy suspicion. Percutaneous aspirate cytology may be diagnostic but may be insufficient to completely exclude cystic malignancy.
Adrenal pseudocyst is a benign lesion. Diagnosis can be made with typical imaging features (wall calcification + cystic content + no enhancement). Surgery may be considered for large or symptomatic lesions.