Microcysts

Microcysts are very small cystic structures found in various tissues and organs. A microcyst is a fluid-filled cavity usually lined by epithelium or ductal remnants, smaller than common cysts detected on routine imaging. They may be solitary or numerous and can be unilocular or part of a more complex, multilocular lesion.

They arise from dilation or disruption of ducts, acini, or glandular structures and can reflect developmental anomalies, inflammation, obstruction, or degenerative change. Most microcysts are incidental and benign; however, their clinical significance depends on their size, location, and association with other pathology. They may cause symptoms if sufficiently large or when they compress nearby structures, and sometimes raise concern for neoplasia when seen with suspicious imaging features.

Diagnosis is based on imaging and, when necessary, tissue sampling. Ultrasound is often the first modality and can show tiny anechoic or hypoechoic spaces; magnetic resonance imaging or computed tomography may delineate walls and contents. In uncertain cases, aspiration or biopsy of the cyst wall may be performed to establish histology.

Organ-specific examples include the kidney, where tiny cysts can be a normal finding with aging or part of polycystic kidney disease; the pancreas, where microcystic serous cystadenoma is a benign tumor composed of many small cysts; and the breast, where microcysts commonly accompany fibrocystic changes and are usually benign.

Management depends on context. Asymptomatic microcysts typically require no treatment beyond observation, while symptomatic, enlarging, or suspicious lesions may warrant drainage, sclerotherapy, or surgical removal. The prognosis reflects the underlying condition rather than the microcysts themselves.