AKT · Endocrine/Breastlow yield

Breast cyst

Fluid-filled benign breast lesion (perimenopausal)

Overview

A fluid-filled, benign breast lump, common in the perimenopausal years (40s–50s). Smooth, sometimes tender, can appear suddenly; confirmed on ultrasound and resolves on aspiration. Bloodstained aspirate or a residual mass after aspiration needs further assessment.

Recognise

Smooth, well-defined, sometimes tender lump; may appear suddenly; often multiple/bilateral; perimenopausal
Ultrasound: well-defined anechoic (fluid) lesion; resolves on aspiration
Associated with fibrocystic change (lumpy, cyclical breast discomfort)

Red flags

BLOODSTAINED aspirate, residual mass after aspiration, or rapid recurrence → image/biopsy (exclude malignancy/intracystic papilloma)

Differentials & how to tell them apart

Fibroadenomasolid, firm, mobile, younger; not fluid on ultrasound/aspiration

Breast cancerhard, irregular, fixed, skin change; complex/solid on imaging

Galactocelemilk-filled cyst during/after lactation

Investigations

Triple assessment with ultrasound; aspiration (simple cysts resolve). Cytology if bloodstained/complex.

Management

Ultrasound + aspiration (simple cysts resolve); image/biopsy if complex or bloody

1Confirm a simple cyst on ultrasound; aspirate if symptomatic (it resolves).Gate: A BLOODSTAINED aspirate, a residual lump after aspiration, or a complex/solid cyst on ultrasound needs biopsy to exclude malignancy/intracystic papilloma
2Recurrent/complex cysts → further imaging/biopsy; reassure for simple cysts.

Aspiration — diagnostic and therapeutic for symptomatic simple cysts

Key points

Perimenopausal smooth lump that's fluid on ultrasound and resolves on aspiration = simple cyst. Blood in the aspirate or a residual mass is the red flag.

Monitor & prognosis

Recurrence; complex features.

Benign.

Source: NICE NG101; CKS Breast