Subserosal leiomyoma is a type of leiomyoma originating from the myometrium and growing toward the serosal surface (peritoneal surface) of the uterus. It constitutes approximately 20-25% of all fibroids. In FIGO classification, it is subclassified as Type 5 (≤50% intramural), Type 6 (<50% intramural), and Type 7 (pedunculated, entirely extraperitoneal/attached to uterus by stalk). Unlike submucosal fibroids, it does not distort the endometrial cavity, so it generally does not cause bleeding symptoms. Symptoms are pressure effects related to size: pelvic pain, bladder/bowel compression, back pain. Pedunculated (Type 7) lesions carry torsion risk — may present with acute abdomen. Broad ligament leiomyoma is a rare variant showing retroperitoneal growth. Parasitic myoma is a pedunculated fibroid that adheres to adjacent structures such as omentum/bowel and develops additional blood supply. MRI is superior to US for evaluating large subserosal and pedunculated fibroids — uterine origin, stalk structure, and adjacent organ relationships are clearly demonstrated.
Age Range
30-55
Peak Age
42
Gender
Female predominant
Prevalence
Common
Subserosal leiomyoma originates from the outer region of the myometrium near the serosal surface and grows toward the peritoneal cavity. Its histopathological structure is identical to intramural leiomyoma (smooth muscle + collagen matrix), but since growth direction is outward, it does not affect the endometrial cavity → weak association with menorrhagia and infertility. As size increases, pelvic pressure symptoms develop: bladder compression → urinary frequency/retention, rectal compression → constipation, sacral nerve compression → back/leg pain. In pedunculated (Type 7) lesions, the fibroid is connected to the uterus by a narrow stalk (pedicle) — this stalk contains single or few feeding vessels. Torsion risk is the most critical complication: rotation of the stalk around its axis → vascular occlusion → hemorrhagic infarction → acute abdominal pain. On MRI, torsioned pedunculated fibroid shows T1 hyperintensity (hemorrhage) + T2 heterogeneity. Broad ligament fibroid is rare and may be supplied by utero-ovarian ligament vessels rather than uterine artery branches → vascular anatomy is critical for surgical planning. Parasitic myoma is a pedunculated fibroid that develops additional vascular supply from adjacent structures (omentum, bowel mesentery) — may arise de novo from released fibroid fragments after laparoscopic myomectomy (iatrogenic parasitic myoma).
Claw sign: normal myometrium (intermediate T2 signal) extending in a claw shape around the base of the exophytic mass (hypointense T2 signal) — pathognomonic finding confirming uterine origin of the mass. Bridging vessel sign: feeding vessels extending from the uterus to the base/stalk of the mass — demonstrated on Doppler or contrast-enhanced MRI. Together, these two findings definitively differentiate subserosal leiomyoma from adnexal masses (ovarian origin).
Hypoechoic/heterogeneous solid mass deforming the uterine contour outward or protruding beyond the uterus. Endometrial cavity is generally normal, showing no distortion. In pedunculated (Type 7) type, mass is connected to uterus by narrow stalk — demonstrating the stalk is critical for diagnosis but may not always be clearly visualized on US. In broad ligament fibroid, mass shows retroperitoneal extension and may be confused with ovary/tube. Large subserosal fibroids may deform the uterus beyond recognition — 'uterus myomatosus' appearance.
Report Sentence
A ___ x ___ x ___ mm hypoechoic solid mass protruding outward from the uterine fundus/corpus is seen with normal endometrial cavity; consistent with subserosal leiomyoma.
Feeding vascular structures extending from uterus to the base/stalk of the mass on color Doppler (bridging vessels) — critical finding confirming uterine origin of the mass. Single or few arteries in stalk visualized in pedunculated type. Peripheral circumferential vascularity may be seen around the mass. Demonstration of this vascular connection is the most valuable Doppler finding for differentiation from adnexal masses.
Report Sentence
Feeding vascular structures extending from the uterus to the base of the mass (bridging vessels) are detected on color Doppler; confirming the uterine origin of the mass.
Hypointense, well-defined mass protruding outward from the uterine serosal surface on T2W. Shows continuity with uterine myometrium — 'claw sign' can also be seen on MRI. Pseudocapsule appears as thin hyperintense ring. In pedunculated type, narrow hypointense stalk clearly shows uterus-myoma connection. Broad ligament fibroid appears as hypointense mass in retroperitoneal space — ureteral deviation and ovarian lateralization may accompany. Heterogeneous signal on T2 in torsioned fibroid (edema + hemorrhage).
Report Sentence
A ___ x ___ x ___ mm hypointense, well-defined exophytic mass protruding from the serosal surface of the uterine fundus/corpus is seen on T2W, showing continuity with myometrium (positive claw sign); consistent with subserosal leiomyoma (FIGO Type ___).
Exophytic mass isointense or slightly hypointense to myometrium on T1W. Homogeneous signal in uncomplicated fibroid. T1 hyperintensity in torsion — methemoglobin accumulation due to hemorrhagic infarction. Less enhancement than myometrium on contrast-enhanced T1; diminished/absent enhancement in torsioned fibroid.
Report Sentence
The exophytic mass shows signal isointense to the myometrium on T1W; no T1 hyperintensity detected, no findings consistent with torsion/hemorrhagic degeneration.
Exophytic mass of soft tissue density protruding outward from the uterus on CT. Less enhancement than myometrium in contrast phase. Calcification is common and diagnostically helpful. Narrow stalk shows uterine origin in pedunculated type. CT is helpful for uterus-ovary differentiation in incidentally detected pelvic masses but limited in tissue characterization compared to MRI. In torsion, vascular occlusion at the stalk may be seen as 'swirl sign'.
Report Sentence
An exophytic mass of soft tissue density measuring ___ x ___ mm protruding outward from the uterus is seen on CT, consistent with subserosal leiomyoma.
No significant diffusion restriction on DWI in uncomplicated subserosal leiomyoma — ADC values are normal or mildly reduced. In torsion, markedly high signal on DWI + low ADC value due to hemorrhagic infarction. DWI is critical for torsion diagnosis and leiomyosarcoma differentiation: diffuse and marked restriction is expected in sarcomatous transformation, while peripheral restriction + central necrosis pattern is seen in torsion.
Report Sentence
No significant diffusion restriction is detected in the exophytic lesion on DWI/ADC map; no findings consistent with torsion or malignant transformation.
Criteria
≤50% of myoma within myometrium, >50% beyond serosa
Distinct Features
Most common subserosal type. Markedly deforms uterine contour. Connected to myometrium by broad base. Intramural depth measurement on MRI mapping important for treatment planning.
Criteria
Less than 50% of myoma within myometrium, majority extraperitoneal
Distinct Features
Connected to myometrium by narrow base. More markedly deforms uterine contour. Suitable for laparoscopic myomectomy.
Criteria
Myoma entirely extraperitoneal, connected to uterus by narrow stalk (pedicle), no intramural component
Distinct Features
Highest torsion risk type. Type most commonly confused with adnexal mass — claw sign and bridging vessels are differentiating. Potential for parasitic myoma development. Suitable for laparoscopic stalk ligation + excision.
Criteria
Subserosal myoma grown between broad ligament leaves, retroperitoneal extension
Distinct Features
Rare variant. Mass in retroperitoneal space → ureteral deviation, ovarian lateralization. May be confused with ovarian tumor. Surgical dissection difficult — risk of ureteral injury. Uterine connection and T2 hypointensity diagnostic on MRI.
Distinguishing Feature
In ovarian fibroma, mass originates from ovary — normal ovarian tissue seen around the mass (ovarian claw sign), no connection to uterus. In subserosal myoma, claw sign is from uterine myometrium, bridging vessels from uterine artery. Both lesions are T2 hypointense — determining organ of origin is the differentiator.
Distinguishing Feature
In ovarian torsion, ovary is enlarged with increased echogenicity due to stromal edema, peripheral follicular arrangement preserved, whirlpool sign in vascular pedicle. In torsioned pedunculated myoma, hypoechoic solid mass with stalk connection to uterus, ovary separately visualized as normal.
Distinguishing Feature
Leiomyosarcoma shows heterogeneous high T2 signal, marked diffusion restriction (low ADC), necrotic areas, irregular borders, rapid growth. Benign subserosal myoma shows homogeneous T2 hypointensity, no DWI restriction, smooth borders, stable size.
Urgency
routineManagement
surveillanceBiopsy
Not NeededFollow-up
12-monthSubserosal leiomyoma is generally asymptomatic or presents with pressure symptoms. Since it does not distort the endometrial cavity, association with bleeding and infertility is weak. Treatment depends on symptom presence and severity: annual US follow-up is sufficient for asymptomatic cases. In symptomatic cases, laparoscopic myomectomy (Type 6-7) or laparotomic myomectomy (large, broad-based) is preferred. UAE may be effective for subserosal fibroids but is contraindicated in pedunculated type due to risk of stalk necrosis and peritonitis. Torsion is an emergency surgical indication. Surgical dissection is difficult in broad ligament fibroids — high risk of ureteral and uterine artery injury, pre-op MRI mapping is mandatory. Fragments should not be left during laparoscopic myomectomy due to risk of parasitic myoma development.
Subserosal leiomyomas usually cause pressure symptoms. Pedunculated types carry torsion risk. Large subserosal myomas may be confused with ovarian masses. MRI assessment of uterine origin and pedicle is important for surgical planning.