[Look-alike ill-demarcated T2-low enlarged uterus]

Fig 1: Look-alike ill-demarcated T2-low enlarged uterus

Tumor-like lesion: Adenomyosis

Tumor: Low-grade endometrial stromal sarcoma

[Adenomyosis]

• Common non-neoplastic disease characterized by the presence of ectopic endometrium within the myometrium
• Affects multiparous, premenopausal women with dysmenorrhea, menorrhagia, and abnormal genital bleeding

[Mimicker: Low-grade Endometrial Stromal Sarcoma: LG-ESS]

• Rare malignant mesenchymal tumor affecting young women
• May mimic adenomyosis, and characteristic myometrial invasion as “Bag of worms” (preserved T2-low smooth muscle bundles within T2-high tumor)
• Diffusion restriction (+)

[Decidualized Adenomyosis]

• Decidualization during pregnancy may also occur in ectopic endometrial tissue in adenomyosis
• Multiple T2-high dilated, decidualized endometrial foci within adenomyosis is observed, which may mimic LG-ESS with “Bag of worms”
• Diffusion restriction (-), T2 shine-through (+)

Fig 2: Look-alike uterus w/ “bag of worms” ?

Fig 3: Decidualized Adenomyosis associated w/ Pregnancy

[Look-alike localized ill-demarcated T2-low areas]

Fig 4: Look-alike localized ill-demarcated T2-low areas

Tumor-like lesion (pseudotumoral lesion): Myometrial contraction

Tumor-like lesion: Focal adenomyosis

• Transient myometrial contraction may be observed as a physiological phenomenon and may appear T2-low mass-like lesion mimicking focal adenomyosis, which disappears in subsequent images. The appearance of lesions changes on kinematic MRI
• Myometrial contraction is common in pregnant uterus because of increased blood supply to the fetus

[Physiologic changes of the uterus during Menstrual cycle]

• The uterus undergoes significant changes depending on its physiological state and menstrual cycle, so a thorough understanding is essential for evaluating uterine lesions

Fig 5: Physiologic changes of the uterus during Menstrual cycle

[Look-alike ovarian cystic masses w/ hematocrit effect]

Fig 6: Look-alike ovarian cystic masses w/ hematocrit effect

Tumor-like lesion: Corpus Luteum Cyst

Tumor: Low-grade Serous ca.

[Corpus Luteum / Corpus Luteum Cyst]

• Corpus luteum (CL) develops from an ovarian follicle during the luteal phase following ovulation
• Corpus luteum cyst (CLC) is a hemorrhagic retention cyst after ovulation. Hypervascular functional epithelium of thick luteinized cell layer may be easily hemorrhagic
• Smooth, thick wall w/ T2 shine-through vs Irregular, thick wall w/ diffusion restriction in cystic carcinoma
• If gets fertilized, the CL continues as CL of pregnancy and will release progesterone. Around week 12, the CL will start to break down
• Ovulation induction by hCG may cause multiple CL
• Occasionally, CL of pregnancy forms CLC, during 1st trimester and shrinks at 2nd trimester; May cause rupture or torsion

Fig 7: Corpus luteum

Fig 8: Corpus luteum (CL) of pregnancy

Fig 9: Corpus luteum cyst

Fig 10: Physiologic changes of the ovary during Menstrual cycle

[Look-alike ovarian T2-low masses]

Fig 11: Look-alike ovarian T2-low masses

Tumor-like lesion: Stromal hyperplasia

Tumor: Fibroma /Thecoma

[Stromal hyperplasia]

• Diffuse enlargement of bilateral ovaries due to stromal hyperplasia (SH). Bilateral T2-low ovarian enlargement
• Prevalent at perimenopause /postmenopause
• Hyperthecosis (HT) is SH with luteinizing cell proliferation in response to increased gonadotropins; may be associated with masculinizing symptoms and menstrual abnormalities due to androgen production

[Look-alike ovarian masses w/ T2-peripheral low /central high]

Fig 12: Look-alike ovarian masses w/ T2-peripheral low /central high

Tumor-like lesion: Fibromatosis

Tumor: Krukenberg tumor

Tumor: Sclerosing stromal tumor

[Fibromatosis]

• Ovarian enlargement in young women affecting one or both ovaries
• Characterized by a proliferation of collagen-producing spindle cells surrounding normal ovarian structures
• Asymptomatic, or menstrual abnormalities, abdominal pain, hirsutism, or virilization
• Diffuse to cortical fibrous thickening exhibits T2-low due to dense stromal proliferation as “black garland”-like appearance. Ovarian follicles and corpus luteum may be preserved within the mass surrounded by the thickened cortex

Fig 13: Ovarian fibromatosis

[Look-alike T2-very high ovarian masses]

Fig 14: Look-alike T2-very high ovarian masses

Tumor-like lesion: Massive Ovarian Edema

Tumor: Krukenberg tumor

[Massive Ovarian Edema]

• Benign enlarged ovary affecting young women
• Intermittent torsion causes partial obstruction of venous /lymphatic drainage, accumulation of edema fluid within the stroma, and ovarian enlargement, T2-prominent high, T2 shine-through (+)
• Lower abdominal pain, intermittent of several months to years’ duration. Virilization in 20% of cases
• Diagnosis is important in selecting ovarian preservation treatment by laparoscopic untwisting or conservative management

Fig 15: Massive ovarian edema

[Transition of Massive ovarian edema and Ovarian fibromatosis]

• There is an argument: enlarged ovary with fibromatosis promotes torsion with subsequent massive ovarian edema, whereas fibromatosis is a “burned-out” stage of a reactive fibroblastic proliferation in massive ovarian edema

Fig 16: Transition of Massive ovarian edema and Ovarian fibromatosis

[Look-alike T2-high mural nodules in endometriotic cyst]

Fig 17: Look-alike T2-high mural nodules in endometriotic cyst

Tumor-like lesion: Decidualized Endometriotic Cyst

Tumor-like lesion: Polypoid Endometriosis

Tumor: Seromucinous Borderline Tumor

[Decidualized Endometriotic Cyst associated with pregnancy]

• Decidualized endometriotic cyst (DE) may manifest as broad-based, flat or polypoid mural nodules w/ smooth contour
• Signal is similar to placenta: prominent T2-high reflecting edematous, vascularized decidualized tissue. DWI-high w/ high ADC (T2 shine-through)

[Mimicker: Seromucinous Borderline Tumor: SMBT]

• Uncommon Müllerian-type tumor arising from endometriosis
• May affect relatively younger patients (30-40’s)
• Papillary mural nodules within endometrioma.
• Prominent T2-high reflecting edematous stroma w/ abundant mucinous material, T2 shine-through (+), mimicking DE
• The greater number and lower height are suggestive of DE, whereas lobulated margin, pedunculated configuration, and T2-low core (43-61%) of mural nodules are suggestive of SMBT

Fig 18: Decidualized endometriotic cyst associated with pregnancy

[Polypoid Endometriosis associated with Endometriotic cyst]

• Rare variant of endometriosis w/ histological features resembling endometrial polyp
• May arise in endometriotic or adenomyotic cysts; forms large, often multiple polypoid masses with extra-mural extension and may invade adjacent organs, simulating infiltrative malignancy
• Edematous tissue may show T2-high, intense CE, T2 shine-through (+), diffusion restriction (-)
• Endometriotic hemorrhagic foci may be present
• Dilated endometrial glands may show solid and microcystic pattern

Fig 19: Polypoid endometriosis arising in endometriotic cyst

[Look-alike bilateral ovarian multilocular cystic masses]

Fig 20: Look-alike bilateral ovarian multilocular cystic masses

Tumor-like lesion: Hyperreactio Luteinalis

Tumor: Bilateral Ovarian Metastases (Colon ca.)

[Hyperreactio Luteinalis]

• Multiple theca lutein cysts caused by increased serum hCG, and hypersensitivity of FSH receptor w/ mutation
• Usually w/ gestational trophoblastic disease or polycyesis, rarely w/ normal pregnancy
• Regresses in size after delivery or removal of causative factors; Usually asymptomatic, occasionally cause torsion, intra-cystic hemorrhage, or rupture
• Marked bilateral ovarian enlargement w/ uniform multiple cysts separated by intervening parenchyma as characteristic “spoke-wheel” appearance
• Residual parenchyma may show T2-high, DWI-high w/ high ADC (T2 shine-through) vs multilocular malignancy w/ diffusion restriction

Fig 21: Hyperreactio luteinalis

Fig 22: Hyperreactio luteinalis (HL)

[Look-alike large ovarian cyst during pregnancy]

Fig 23: Look-alike large ovarian cyst during pregnancy

Tumor-like lesion: Large solitary luteinized follicle cyst

Tumor: Cystadenoma

[Large solitary luteinized follicle cyst of pregnancy and puerperium (LSLFCPP)]

• Unilateral, large, thin-walled, solitary cysts as an abnormal reaction to hCG during pregnancy; may persist beyond the second trimester (whereas functional cysts may spontaneously regress), mimicking cystic neoplasms
• May progress during postpartum period (reaction to pituitary gonadotropin)
• The large size (often > 20 cm) and rapid growth are suggestive

Pregnancy-related tumor-like lesions

Fig 24: Pregnancy-related tumor-like lesions

[Look-alike cystic masses w/ mural nodule]

Fig 25: Look-alike cystic masses w/ mural nodule

Tumor-like lesion: Peritoneal inclusion cyst

Tumor: Ovarian cancer

[Peritoneal inclusion cyst]

• Extensive pelvic adhesions w/ impaired fluid absorption due to surgical procedure, trauma, inflammation or endometriosis
• Trap the intra-peritoneal fluid and form the pseudocystic lesion w/ irregular margins defined by the adjacent pelvic structures, including normal ovaries
• Occasionally multiloculated and hemorrhagic, mimicking tumor; the ovary in the pseudocyst may simulate a solid tumoral component of cystic tumor
• May resolve spontaneously, and when asymptomatic, observation is initially chosen; therefore, differentiation from neoplastic lesions is crucial

[Look-alike Cul-de-Sac masses]

Fig 26: Look-alike Cul-de-Sac masses

Tumor-like lesion: Polypoid Endometriosis

Tumor: Dissemination of Cancer

[Polypoid endometriosis in the peritoneal cavity]

• Forms large, often multiple polypoid masses simulating malignant implants
• May invade adjacent organs and may mimic infiltrative malignant tumors
• Edematous tissue may show T2-high, intense CE, T2 shine-through (+)
• Surrounding T2-low adhesive fibrous tissue (black rim sign) is suggestive of polypoid endometriosis

Fig 27: Polypoid endometriosis in the peritoneal cavity

[Look-alike Bowel masses]

Fig 28: Look-alike Bowel masses

Tumor-like lesion: Bowel Endometriosis

Tumor: Bowel Cancer

[Less common site and rare site endometriosis]

• The endometrial tissue infiltrates the adjacent fibromuscular tissue and induces smooth muscle proliferation and fibrous reaction, resulting in the formation of T2-low solid masses
• Hemorrhagic foci may be observed
• Diffusion restriction (-)

Fig 29: Less common site and rare site endometriosis

[Miscellaneous lesions]

[Gossypiboma or gauzeoma]

• Gossypiboma or gauzeoma (foreign body granuloma) is a mass of cotton (sponge or gauze) within the body left accidentally during a surgical procedure
• Well-defined mass w/ T2-low fibrous capsule; Central T2-low whorled stripes reflecting gauze fibers
• May mimic ovarian tumor, episodes of the surgery and identification of normal ovaries may also lead to the diagnosis

[After HSG w/ oil soluble contrast medium]

• Inverted fat-fluid levels may be observed in the pelvic cavity or dilated fallopian tube after hysterosalpingography w/ oil soluble contrast medium (specific gravity >1) for infertility screening
• May mimic fat-containing tumor (teratoma etc.), but NOT pathologic finding

Fig 30: Miscellaneous lesions