Endometrioma (chocolate cyst) is a cystic lesion formed by ectopic endometrial tissue implanted within the ovary, producing recurrent cyclic hemorrhage. Seen in 17-44% of endometriosis patients and most common in premenopausal women (age 25-40). Characterized on ultrasound by homogeneous low-level internal echoes (ground-glass appearance). On MRI, T1 hyperintense signal (blood products) and T2 shading (pathognomonic — gradual T2 signal loss) are diagnostic findings. Shows no internal enhancement. May be bilateral (50%). Carries endometriosis-associated infertility, pelvic pain, and malignancy risk (endometrioid/clear cell carcinoma, <1%).
Age Range
20-45
Peak Age
35
Gender
Female predominant
Prevalence
Common
Endometrioma forms when ectopic endometrial tissue implanted on the ovarian surface produces recurrent hemorrhage in response to the menstrual cycle. Each menstrual cycle, the endometrial tissue proliferates, secretes, and sheds — but the bleeding cannot be expelled and accumulates within the cyst. Accumulated old blood products (hemosiderin, methemoglobin, denatured protein) from recurrent hemorrhages form dark brown 'chocolate-like' fluid. This concentrated, high-protein, iron-rich fluid appears as homogeneous low-level internal echoes (ground-glass) on ultrasound — internal echoes originate from cellular debris and protein aggregates in the fluid. On MRI, T1 bright signal is from methemoglobin. T2 shading is the pathognomonic finding of endometrioma: increasing iron concentration (hemosiderin + denatured protein) from accumulated recurrent hemorrhages shortens T2 relaxation time — creating gradual T2 signal loss within the cyst (more prominent centrally to peripherally or in dependent portion). This phenomenon is not seen in single hemorrhage (hemorrhagic cyst) because iron accumulation does not reach sufficient concentration.
Gradual signal loss (shading) within the cyst on MR T2-weighted sequences is the pathognomonic signature finding of endometrioma. This phenomenon results from progressive shortening of T2 relaxation time by increasing iron (hemosiderin/ferritin) and denatured protein concentration from accumulated recurrent cyclic hemorrhages. In single hemorrhage (hemorrhagic cyst), this concentration is not reached and T2 shading is not seen. Presence of T2 shading confirms endometrioma diagnosis and is the most valuable MR finding in differentiating from hemorrhagic cyst. Shading is seen gradually in the dependent portion or from center to periphery within the cyst.
Homogeneous, low-to-medium level diffuse internal echoes within the cyst. Described as 'ground-glass' appearance. Echoes are homogeneously distributed without internal septa or solid component.
Report Sentence
A ___ x ___ mm cystic lesion with homogeneous low-level internal echoes (ground-glass appearance) is seen in the ovary, consistent with endometrioma.
No vascular flow detected within the cyst on color Doppler. Minimal vascularity may be present in the cyst wall. No internal enhancement.
Report Sentence
No vascular flow is detected within the cyst on color Doppler examination, with no findings suggesting solid neoplastic component.
Gradual signal loss (shading) within the cyst on T2-weighted sequences. Cyst is not homogeneously T2 hyperintense — prominent hypointensity seen in dependent portion or centrally. Characteristic 'shading' pattern.
Report Sentence
The lesion shows characteristic T2 shading (gradual signal loss) on T2-weighted sequences, strongly supporting the diagnosis of endometrioma.
Hyperintense (bright) signal on T1-weighted sequences — recurrent hemorrhage products (methemoglobin). Signal PRESERVED on fat-saturated sequence — confirms blood, not fat.
Report Sentence
The lesion shows hyperintense signal on T1-weighted sequences with preserved signal on fat-saturated sequence; consistent with blood products (endometrioma).
Multiple bilateral T1 hyperintense cystic lesions — endometriosis 'fingerprint' finding. 'Kissing ovaries' (bilateral endometriomas adherent to each other) may be seen.
Report Sentence
Multiple T1 hyperintense cystic lesions are observed in bilateral ovaries, consistent with endometriotic cysts.
Cystic lesion showing increased density relative to water (25-50 HU) on CT. Content homogeneous, wall thin to moderately thick. No enhancement.
Report Sentence
A homogeneous cystic lesion with increased density (___ HU) is seen in the adnexal region, suggesting proteinaceous/hemorrhagic content; MRI correlation recommended for endometrioma diagnosis.
Criteria
Unilocular, homogeneous ground-glass echoes, T1 bright, T2 shading positive, no internal enhancement. Most common form.
Distinct Features
Diagnosis is straightforward — all classic findings are present. Follow-up or surgery decision based on size, symptoms, and fertility status.
Criteria
Enhancing solid nodule or papillary projection in endometrioma wall. Solid component showing vascularity. Carries suspicion of malignant transformation.
Distinct Features
Although malignant transformation risk is <1%, endometrioid or clear cell carcinoma must be excluded when enhancing wall nodule is present. Enhancement, DWI restriction, and size of nodule are evaluated on MRI. Requires surgical exploration.
Criteria
Bilateral endometriomas ('kissing ovaries'), deep endometriosis (rectovaginal septum, uterosacral ligament), peritoneal implants, and pelvic adhesions accompany.
Distinct Features
MRI pelvic endometriosis mapping should be performed. Deep endometriosis is seen as T2 hypointense nodules. Detailed MRI protocol needed for surgical planning. Fertility preservation is important.
Distinguishing Feature
Hemorrhagic cyst does not show T2 shading (single hemorrhage, insufficient iron accumulation). Endometrioma shows T2 shading (recurrent hemorrhage, concentrated iron accumulation). Hemorrhagic cyst resolves in 6-8 weeks, endometrioma persists. On US, hemorrhagic cyst shows reticular pattern, endometrioma shows homogeneous ground-glass echoes.
Distinguishing Feature
Dermoid cyst is T1 bright and loses signal on fat-sat (fat). Endometrioma is T1 bright and preserves signal on fat-sat (blood). On CT, dermoid shows negative density (-20 to -130 HU), endometrioma shows positive density (25-50 HU). Dermoid has calcification (teeth/bone) and Rokitansky nodule, absent in endometrioma.
Distinguishing Feature
Serous carcinoma shows solid enhancing components, papillary projections, and internal vascularity. Ascites and peritoneal implants may accompany. Endometrioma has no internal enhancement and T2 shading is positive. However, if enhancing wall nodule is present in atypical endometrioma, malignant transformation (endometrioid carcinoma) must be excluded.
Urgency
routineManagement
medicalBiopsy
Not NeededFollow-up
6-monthEndometrioma is a benign lesion associated with endometriosis. Treatment decision is based on size, symptoms (pelvic pain, dyspareunia), fertility status, and malignancy suspicion. 6-month US follow-up is acceptable for small (<4 cm), asymptomatic endometriomas. Medical therapy (OCP, progestins, GnRH analogues) is used for pain control. Surgery (cystectomy) is planned for >4 cm, symptomatic or growing lesions, pre-fertility, or when atypical features are present (enhancing wall nodule). Although malignant transformation risk is <1%, malignancy (endometrioid/clear cell carcinoma) must be excluded in postmenopausal women or rapidly growing lesions. Cystectomy is preferred for bilateral endometrioma to preserve ovarian function. Multidisciplinary approach is needed when deep endometriosis accompanies.
Endometriomas are associated with endometriosis. Dysmenorrhea, chronic pelvic pain, and infertility are common. Malignant transformation risk is low (0.7-1%) but caution is needed especially in lesions >9 cm and with developing solid components. New enhancing solid component suggests malignant transformation.