Breast cysts

Overview

•Most common cause of a discrete breast lump; affect ~7% of Western women

•Peak incidence: ages 30-50, perimenopausal period; new cysts uncommon post-menopause unless on HRT

Presentation

•Smooth, well-circumscribed, mobile lump - may be fluctuant if superficial and tense

•Tender - particularly premenstrual; size varies with menstrual cycle (enlarges premenstrually, reduces after menstruation)

•Can be single or multiple, unilateral or bilateral

•Acute rupture - sudden focal pain and tender palpable mass

Investigations

Any discrete breast lump requires triple assessment: clinical examination + imaging + tissue sampling where indicated.

🥇 First-line

•Ultrasound (USS) - preferred in women under 40 and for characterising palpable lumps at any age. Simple cyst: anechoic, thin smooth wall, posterior acoustic enhancement

•Mammography - in women aged 35 and over alongside USS; may show a circumscribed density

🏆 Gold standard

•Fine needle aspiration (FNA) or core biopsy - diagnostic and therapeutic. Aspirated fluid typically straw-coloured or greenish; send for cytology only if bloodstained or macroscopically abnormal

🚨

Two findings on aspiration mandate urgent further investigation: (1) bloody aspirate - send for cytology, consider core biopsy; (2) rapid refilling after aspiration - biopsy or excision warranted.

Management

•NICE 2-week wait referral: any woman aged 30 or over with an unexplained breast lump; non-urgent referral if under 30

•First-line - asymptomatic simple cyst: reassurance and observation - many self-resolve

•First-line - symptomatic cyst: FNA - both diagnostic and therapeutic; straw-coloured/greenish fluid does not require routine cytology

🥈 Second-line

•core needle biopsy - if bloody fluid, rapid refill, or complex cyst on imaging

🥉 Third-line

•surgical excision - recurrent cysts after aspiration, enlarging complex cysts, or malignancy cannot be excluded

•Cyclical mastalgia: well-fitting bra, ibuprofen; refractory cases - tamoxifen or danazol under specialist guidance

Complications and Prognosis

•Recurrence after aspiration - common but benign; repeat aspiration or excision if troublesome

•Intracystic haemorrhage - rapidly enlarging painful lump; requires aspiration and cytology

•Slightly increased lifetime risk of breast cancer - particularly with complex or multiple cysts; continue breast awareness and routine NHS screening from age 50

•Prognosis excellent - majority of simple cysts self-resolve, especially at menopause