What is an adnexal cyst?

What is an Adnexal Cyst?

An adnexal cyst is a fluid-filled sac located in the adnexa—the anatomical region adjacent to the uterus that includes the ovaries, fallopian tubes, and surrounding connective tissues. 1

Anatomical Location and Definition

• Adnexal cysts arise from structures in the adnexa, which encompasses the ovaries, fallopian tubes, and adjacent pelvic tissues 1
• These masses are predominantly cystic in nature, though they can also be solid or mixed cystic-solid 1
• The term "adnexal" distinguishes these from purely ovarian masses, as they may originate from any structure in this region 2, 3

Common Types of Adnexal Cysts

Functional (Physiologic) Cysts

• Simple cysts are the most common type, representing benign fluid collections with smooth walls and no solid components 1, 4
• In premenopausal women, simple cysts establish a benign process in 98.7% of cases 1
• In postmenopausal women, simple cysts establish a benign process in 100% of cases 1
• Most functional cysts in premenopausal women resolve spontaneously without intervention 1
• Hemorrhagic cysts display characteristic spiderweb-appearing or retracting clot patterns with peripheral vascularity on ultrasound 1

Non-Functional Benign Cysts

• Endometriomas show low-level internal echoes, mural echogenic foci, or nonvascular solid attenuating components 1
• Teratomas (dermoid cysts) contain echogenic attenuating components or small horizontal interfaces, representing fat, solid, and calcified tissue 1
• Hydrosalpinges appear as tubular cystic masses with or without folds, originating from the fallopian tube 1
• Peritoneal inclusion cysts take the shape of underlying pelvic spaces and are located adjacent to or surrounding a functioning ovary 1
• Paraovarian or paratubal cysts account for approximately 6% of surgically managed adnexal masses 1

Pregnancy-Specific Cysts

• Hyperreactio luteinalis presents as bilateral ovarian enlargement with multiple theca lutein cysts, typically in the third trimester, and spontaneously regresses after delivery 1
• Approximately three-quarters of incidentally identified adnexal masses in pregnancy are simple cysts less than 5 cm 1

Clinical Significance and Malignancy Risk

• The overwhelming majority of adnexal cysts are benign, with malignancy occurring in approximately 2% of cases during pregnancy 1
• Simple unilocular cysts have an extremely low malignancy risk of less than 0.4% 1
• Cysts with a single thin septation less than 3 mm are considered benign 1
• Multiple septations without papillary projections or solid components are unlikely to be malignant 1
• The risk of acute complications such as torsion or cyst rupture is only 0.2% to 0.4% 5

Diagnostic Approach

• Transvaginal ultrasound is the essential initial imaging modality for evaluating adnexal cysts 1, 5
• Color or power Doppler should be included to differentiate true solid components from debris and assess vascularity 1
• For indeterminate masses on ultrasound, MRI with intravenous contrast becomes the modality of choice 1, 5
• CT is not indicated for routine workup due to poor soft-tissue discrimination, except for cancer staging 1

Management Based on Characteristics

Premenopausal Women

• Simple cysts ≤3 cm require no follow-up 6
• Simple cysts >3 cm to ≤5 cm require no additional management 6
• Simple cysts >5 cm but <10 cm warrant follow-up ultrasound in 8-12 weeks 6

Postmenopausal Women

• Simple cysts <3 cm require no follow-up due to extremely low malignancy risk 5
• Simple cysts occur in 17-24% of postmenopausal women and are not related to hormonal therapy 1, 5
• Natural history shows 53% disappear completely, 28% remain constant, and only small percentages change in size 1, 5

Key Clinical Pitfalls to Avoid

• Do not mistake pedunculated fibroids for adnexal cysts—always identify normal ovaries and trace blood supply from uterine vessels 1, 5
• Do not rely solely on CA-125 levels—this marker performs worse than ultrasound in distinguishing benign from malignant lesions and may be low with borderline tumors 1, 5
• Do not skip color Doppler evaluation—it is essential for differentiating true solid components from debris within cysts 1, 5
• Do not fail to recognize torsion signs—enlarged ovary (>4 cm or volume >20 cm³), absent or abnormal venous flow, or absent arterial flow require urgent surgical intervention 6