Table 1.

Comparison of various radiological and histological characteristics of cystic adrenal lesions

Common differentials of cystic adrenal lesions
	Radiological features	Histopathological features
Pseudocyst	CT—well-demarcated round or oval mass with fluid density. Similarity to complex cyst makes it difficult to differentiate from necrosis, metastasis or abscess MRI is better as it detects intracystic haemorrhage (hyperintense on T1/T2)	Thick walled Dense hyalinised connective tissue with focal calcifications entrapped cortical cells in cyst wall. No endothelial lining. Haemorrhage and haemosiderin common
Endothelial cysts	CT—low density (<20 HU) masses with smooth borders and thin walls	Smooth flattened endothelial lining, filled with clear/milky fluid. Absent proliferating endothelium
Epithelial cysts	CT—similar to endothelial cysts	Smooth, flattened wall lined with true epithelium
Parasitic cysts	CT—hydatid sand, floating membranes, daughter cysts, septal/mural calcifications	Wall and cyst contain eosinophils Calcified parasite may be found in the cyst
Adenomas	CT— <10 HU on non contrast CT; <30 HU on CECT; 10-minute delayed CT washout >50%31 MRI—high intracellular lipid leads to drop in signal relative to spleen/liver on chemical shift imaging in MRI. Adrenal:spleen ratio of <0.70 is diagnostic 32 33	Cells are larger with different foamy cytoplasm and distinct cell borders Balloon cells with enlarged lipid-rich cytoplasm may be seen34
Adrenocortical tumours	CT—wall thickness >5 mm with wall enhancement, thick rim and stippled central calcification35	Encapsulated tumour with variably sized nests, large sheets and trabeculae. Large cells with clear to eosinophilic granular cytoplasm present. IGF2 overexpression seen36
Pheochromocytoma	CT—tumour rim enhancement associated with central cystic mass37 High signal intensity on T2 MRI—‘light bulb sign’ MIBG has 95%–100% specificity	Nested/trabecular/solid arrangement of large polygonal vacuolated cells38 Chromogranin A, synaptophysin and S100 positive
Metastasis	CT—ill-defined heterogeneous echotexture with thick enhancing rim on contrast MRI—low T1/high T2 signal. Does not drop signal on opposed-phase MRI (unlike adenoma)39	Morphologically similar to the primary tumour
Lipoma/myolipoma	Gross fat on CT/MRI Can demonstrate flow on Doppler Pseudo-capsule present	Mixture of mature adipocytes and extramedullary haematopoietic cells with marked increase in megakaryocytes40 (No haematopoietic cells in lipoma)

CECT, contrast-enhanced CT; MIBG, metaiodobenzylguanidine.