Breast simple cyst is one of the most common benign lesions of the breast and is a fluid-filled cavity developing from terminal ductal lobular units (TDLU). Most common in women aged 35-50 with peak incidence in the perimenopausal period. Breast cysts can be found in approximately 50% of women; most are clinically silent and detected incidentally. Exhibits hormonal sensitivity; size fluctuations may occur with the menstrual cycle and spontaneous resolution may occur after menopause (in patients not using HRT). On ultrasonography, anechoic internal content, thin smooth wall, posterior acoustic enhancement, and sharp posterior wall delineation criteria are sufficient for simple cyst diagnosis and classified as BI-RADS 2 (benign). On mammography, appears as a round/oval, circumscribed, equal-density mass but cyst-solid mass differentiation cannot be made by mammography alone — supplemental US is indicated. Simple cysts carry no malignancy risk and require no treatment; aspiration may be performed for symptomatic cysts.
Age Range
30-60
Peak Age
45
Gender
Female predominant
Prevalence
Very Common
Breast simple cysts develop during the lobular involution process of the terminal ductal lobular unit (TDLU). While secretory activity continues in the distal portion of the lobular unit, obstruction occurs in the proximal draining duct (due to fibrosis, cellular debris, or epithelial hyperplasia) and fluid accumulation begins in the lumen. The cyst wall is lined with a single layer of flattened or apocrine metaplastic epithelium; this epithelium can actively secrete and determines the composition of cyst fluid. Exhibits hormonal sensitivity due to estrogen receptor expression — secretion increases with progesterone effect during the luteal phase of the menstrual cycle and cyst size enlarges. Anechoic appearance on ultrasound reflects the homogeneity of fluid and absence of solid components or debris — sound waves transmit through fluid without scattering. Posterior acoustic enhancement results from the much lower sound wave attenuation of fluid compared to solid tissue — tissues behind the cyst appear brighter than normal. Thin smooth wall indicates the fibrous capsule is intact and single-layered.
The coexistence of completely anechoic internal content, thin smooth wall, and prominent posterior acoustic enhancement on ultrasound is pathognomonic for simple cyst diagnosis and confirms BI-RADS 2 classification. Absence of any element of this triad (e.g., low-level internal echoes, thick wall, or mural nodule) requires reclassification of the lesion as 'complicated' or 'complex' cyst.
Completely anechoic (echo-free) internal content with thin smooth wall, round or oval lesion. Prominent posterior acoustic enhancement is observed. Lateral edge shadows (edge refraction/refractive shadowing) may be seen at cyst margins. No solid component, debris, thick septation, or mural nodule is present within the internal structure. When all four criteria (anechoic, thin wall, posterior enhancement, no internal echoes) are met together, simple cyst diagnosis is confirmed and classified as BI-RADS 2.
Report Sentence
A completely anechoic, thin smooth-walled round lesion with prominent posterior acoustic enhancement is seen in the breast; no solid component or debris is detected within the internal structure; findings are consistent with simple cyst and assessed as BI-RADS 2.
Bilateral thin acoustic shadowing (edge refraction artifact or refractive shadowing) is observed at cyst margins. This artifact occurs due to refraction of sound waves at the round border of the cyst and is an additional clue helpful in recognizing cystic lesions. Lateral shadows are not seen in solid masses — they are prominent only at fluid-solid tissue transitions.
Report Sentence
Characteristic refractive shadowing artifact is observed at the lateral edges of the lesion, supporting its cystic nature.
On mammography, simple cyst appears as a round or oval, circumscribed, equal-density mass. Halo sign may be present. Cyst-solid mass differentiation cannot be made by mammography because both demonstrate similar X-ray attenuation. Therefore, supplemental US is indicated for every circumscribed mass detected on mammography. Bilateral/multiple cysts are common and should be evaluated the same way.
Report Sentence
Mammography demonstrates a round, circumscribed, equal-density mass; supplemental ultrasonographic evaluation is recommended for cyst-solid mass differentiation.
No vascularity is observed within the simple cyst on color and power Doppler examination — completely avascular. No significant vascularity is expected in the cyst wall or surrounding area. Detection of any Doppler signal within the cyst suggests the presence of an intracystic solid component (intracystic carcinoma or intraductal papilloma) and requires upgrading of the BI-RADS category.
Report Sentence
The lesion is completely avascular on color Doppler examination; no vascularity is detected within the cyst or its wall; this finding supports simple cyst diagnosis.
On breast MRI, simple cyst demonstrates homogeneous and markedly hyperintense signal on T2-weighted sequences — equivalent to fluid signal. Hypointense on T1-weighted sequences (proteinaceous cyst fluid may show T1 hyperintensity but this is classified as 'complicated cyst'). Shows no enhancement on contrast-enhanced sequences — presence of wall or internal enhancement warrants exclusion of complex cyst or intracystic neoplasm.
Report Sentence
Breast MRI reveals a markedly T2-hyperintense, T1-hypointense, non-enhancing lesion; findings are consistent with simple cyst.
Criteria
Size <3 mm. Usually found in large numbers and clustered. Difficult to individually distinguish on US, may appear as a hypoechoic area in clusters.
Distinct Features
No clinical significance; part of fibrocystic changes; usually not visible on mammography; aspiration is not indicated.
Criteria
Size ≥3 mm. Easily detected by US and simple cyst criteria are evaluated. May be palpable (usually >1 cm). May show size fluctuation with menstrual cycle.
Distinct Features
Definitive diagnosis by US; aspiration may be performed when palpable and symptomatic; recurrence after aspiration is common (25-30%); no malignancy risk.
Criteria
Thin wall and posterior enhancement present but low-level homogeneous internal echoes (debris/protein/blood products) in internal structure. No septa, mural nodule, or solid component. Classified as BI-RADS 3.
Distinct Features
Differs from simple cyst by presence of internal echoes; may show T1 hyperintensity on MRI (proteinaceous/hemorrhagic content); 6-month short-interval follow-up US recommended; malignancy risk is very low (<2%).
Distinguishing Feature
Complex cyst contains thick wall, thick septation, intracystic solid component, or mural nodule — does not meet the anechoic/thin wall criteria of simple cyst. Classified as BI-RADS 4 and requires biopsy.
Distinguishing Feature
Fibroadenoma is a hypoechoic solid mass — unlike simple cyst, it produces internal echoes and is not anechoic. However, posterior acoustic enhancement may be seen in both; presence of solid structure (internal echoes) is the fundamental distinguishing criterion.
Distinguishing Feature
Galactocele is a milk retention cyst seen during lactation; may show fat-fluid level on US or appear homogeneously echogenic. Simple cyst is completely anechoic while galactocele frequently contains internal echoes. Clinical history (lactation/breastfeeding) is distinguishing.
Distinguishing Feature
Intraductal papilloma appears as a vascularized solid nodule within a dilated duct — unlike simple cyst, internal solid component and Doppler flow are present. Associated with bloody nipple discharge.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upSimple cyst is a completely benign lesion with no malignancy risk. Simple cysts classified as BI-RADS 2 require no follow-up or biopsy. US-guided aspiration may be performed for symptomatic cysts (pain, tenderness); aspirated cyst fluid should be clear and serous — bloody aspirate requires cytological examination. Recurrence after aspiration is common (25-30%). When multiple cysts are present, the term fibrocystic changes is used and routine screening program continues. In cases where simple cyst criteria are not fully met on US (low-level internal echoes = complicated cyst), short-interval follow-up or aspiration is recommended.
Simple cysts are benign lesions classified as BI-RADS 2. No treatment is required. Aspiration can be performed for symptomatic large cysts. There is no risk of malignant transformation.