Gastric leiomyoma is a benign mesenchymal tumor originating from smooth muscle cells of the muscularis mucosae or muscularis propria layer. Before GIST was identified, it was considered the most common gastric mesenchymal tumor; currently differentiated from GIST by immunohistochemistry (KIT/CD117 negative, desmin and SMA positive). It constitutes approximately 1-2% of gastric mesenchymal tumors — many cases previously classified as GIST are now recognized as true leiomyomas. Usually asymptomatic and incidentally detected; rarely may cause gastrointestinal bleeding or obstruction. On CT, it appears as a well-defined, homogeneous, moderately enhancing submucosal mass in the gastric wall, and unlike GIST, does not show central necrosis, cavitation, or aggressive behavior.
Age Range
30-70
Peak Age
50
Gender
Equal
Prevalence
Uncommon
Leiomyoma originates from the smooth muscle layers of the gastric wall (muscularis mucosae or muscularis propria) and is a slow-growing, well-defined tumor. Histologically, it consists of spindle-shaped smooth muscle cells with eosinophilic cytoplasm and extremely low mitotic activity (<5 mitoses/50 HPF, usually <1). Unlike GIST, it does not carry KIT or PDGFRA mutations — therefore it does not respond to tyrosine kinase inhibitors (imatinib); instead, smooth muscle markers such as desmin, smooth muscle actin (SMA), and h-caldesmon are positive. The homogeneous structure of the tumor results from the monomorphic cell population and is reflected as homogeneous enhancement on CT/MRI; necrosis and hemorrhage are extremely rare unlike GIST because the tumor grows very slowly and vascular supply is adequate for nourishment. Muscularis mucosae-origin leiomyomas are generally small (<2 cm) and intraluminal, while muscularis propria-origin ones can be larger with both intraluminal and exophytic growth. Malignant transformation (leiomyosarcoma) is exceedingly rare, characterized by increased mitotic activity.
On CT, a well-defined, homogeneous, moderately enhancing submucosal mass in the gastric wall — absence of necrosis, cavitation, and hemorrhage is the most reliable imaging finding distinguishing from GIST and favoring leiomyoma.
In the arterial phase, leiomyoma shows moderate, homogeneous enhancement. Compared to the intense arterial enhancement of GIST, leiomyoma's enhancement is less intense — reflecting its lower vascularity. The mass is well-defined, round or oval, showing continuity with the gastric wall. Small leiomyomas (<2 cm) may appear as intraluminal polypoid masses, larger ones as intramural or exophytic masses. The most important feature is homogeneity — central necrosis, hemorrhage, and cavitation seen in GIST are not present in leiomyoma.
Report Sentence
A well-defined, homogeneous, moderately enhancing submucosal mass measuring [X] cm is noted in the gastric wall, consistent with leiomyoma.
In the portal venous phase, leiomyoma maintains homogeneous enhancement and may even show mildly progressive enhancement — no washout is observed. This differs from the washout pattern in GIST. Mass margins are clearly visible in the portal phase as well. Relationship with surrounding gastric wall — continuity or obtuse angle — is best assessed in the portal phase. Perigastric fat planes are preserved without signs of malignancy.
Report Sentence
In the portal venous phase, the mass maintains homogeneous enhancement without washout; preserved perigastric fat planes are consistent with benign pathology.
On EUS, leiomyoma appears as a hypoechoic, well-defined, homogeneous submucosal mass. Muscularis mucosae-origin leiomyomas arise from the 2nd layer (hypoechoic), muscularis propria-origin from the 4th layer (hypoechoic). Leiomyoma and GIST may appear similar on EUS but leiomyoma's homogeneity and small size (<3 cm) are clues favoring benign nature. Internal echoes are homogeneous without cystic areas, calcification, or necrotic areas. Overlying mucosa is intact with 'bridging fold' pattern.
Report Sentence
On EUS, a [X] mm hypoechoic, homogeneous, well-defined submucosal mass originating from the [2nd/4th] layer is seen in the gastric wall; consistent with leiomyoma.
On MRI, leiomyoma appears as a homogeneous mass with low-intermediate signal intensity on T2-weighted sequences. Smooth muscle tissue shows short T2 relaxation time, therefore isointense or mildly hyperintense to muscle tissue. On T1-weighted sequences, low-intermediate signal with homogeneous moderate enhancement on post-contrast. Leiomyoma's low-intermediate T2 signal and homogeneity are distinguishing compared to GIST's frequently high T2 signal (necrosis, edema) and heterogeneous enhancement. No or minimal diffusion restriction on DWI.
Report Sentence
On MRI, a [X] cm submucosal mass with low-intermediate T2 signal intensity and homogeneous moderate post-contrast enhancement is seen in the gastric wall; consistent with leiomyoma.
In the delayed phase, leiomyoma maintains or slightly increases enhancement — progressive enhancement pattern. This reflects contrast accumulation in the interstitial fibrous structure of smooth muscle tissue. In GIST, washout or heterogeneous enhancement is more prominent in the delayed phase. Leiomyoma's maintenance of homogeneous enhancement in the delayed phase is a common feature of fibrous/smooth muscle-rich benign tumors and shows a similar pattern to schwannoma.
Report Sentence
In the delayed phase, the mass maintains homogeneous enhancement with a progressive enhancement pattern, consistent with benign smooth muscle tumor (leiomyoma).
On DWI, leiomyoma shows no or minimal diffusion restriction. ADC values are high (>1.2 × 10⁻³ mm²/s), significantly higher compared to malignant submucosal tumors (GIST, leiomyosarcoma). This feature provides additional information in benign-malignant differentiation. High ADC values reflect leiomyoma's low cellular density and orderly cell arrangement — free diffusion of water molecules in the extracellular space is facilitated.
Report Sentence
No diffusion restriction is observed in the mass on DWI with high ADC values; this finding is assessed in favor of benign smooth muscle tumor.
Criteria
Originates from the 2nd layer (muscularis mucosae — hypoechoic) on EUS. Generally small (<2 cm), intraluminal polypoid mass. Appears as submucosal elevation or small polyp on endoscopy. More common than muscularis propria-origin.
Distinct Features
Endoscopic resection (EMR/ESD) usually possible and sufficient. Recurrence risk minimal. May be difficult to detect on CT due to small size — EUS more sensitive. Malignant transformation risk negligibly low.
Criteria
Originates from the 4th layer (muscularis propria — hypoechoic) on EUS. Can be larger (2-5 cm), may show intramural or exophytic growth. More challenging to distinguish from GIST as origin layer is the same.
Distinct Features
Surgical resection may be required (laparoscopic wedge resection). EUS-FNA with immunohistochemistry (KIT negative, desmin/SMA positive) provides definitive differential diagnosis. Homogeneity and small-medium size are most important imaging clues for distinguishing from GIST.
Criteria
The esophagogastric junction and cardia region is the most common location for leiomyomas (50% of GI leiomyomas are esophageal). Lower esophageal and cardia-origin leiomyomas may protrude into the gastric lumen. Dysphagia is the most common symptom.
Distinct Features
Well-defined submucosal filling defect in the cardia region on barium study and CT. Origin layer and size assessed with EUS. Surgical enucleation or laparoscopic resection for large lesions (>3 cm). Differential: GIST, schwannoma, granular cell tumor.
Distinguishing Feature
GIST shows intense arterial enhancement, heterogeneous internal structure, central necrosis/cavitation, and washout; leiomyoma shows moderate homogeneous enhancement, absence of necrosis, and progressive enhancement. Definitive differentiation is by immunohistochemistry (GIST: KIT+, leiomyoma: desmin/SMA+).
Distinguishing Feature
Schwannoma shows very high T2 signal and marked delayed enhancement (Antoni B areas); leiomyoma shows low-intermediate T2 signal. Schwannoma is S-100 positive, leiomyoma desmin/SMA positive. Both may be homogeneous and well-defined.
Distinguishing Feature
Lipoma is a submucosal mass with homogeneous fat density (-70 to -120 HU) without enhancement; leiomyoma is of soft tissue density with moderate enhancement. Density measurement provides definitive differential diagnosis.
Distinguishing Feature
Carcinoid shows intense arterial enhancement and frequently multiple lesions; leiomyoma shows moderate enhancement and is usually solitary. Carcinoid originates from the 2nd/3rd layer, leiomyoma from the 2nd or 4th layer. Carcinoid shows somatostatin receptor uptake (DOTATATE PET).
Urgency
routineManagement
surveillanceBiopsy
NeededFollow-up
12-monthGastric leiomyoma management depends on size, symptoms, and GIST exclusion. For asymptomatic <2 cm lesions, EUS surveillance (12-24 months) is sufficient. For symptomatic or >2 cm lesions, EUS-FNA with immunohistochemistry (KIT/CD117 negative, desmin/SMA positive) is recommended to exclude GIST. Endoscopic resection (EMR/ESD) may be sufficient for small muscularis mucosae-origin lesions. Laparoscopic wedge resection or surgical enucleation is preferred for muscularis propria-origin or large (>3 cm) lesions. Malignant transformation (leiomyosarcoma) risk is extremely low (<1%). Recurrence after complete resection is very rare and routine follow-up is generally not needed.
Gastric leiomyoma is a benign tumor with no risk of malignant transformation. Differentiation from GIST is clinically important as treatment approaches differ. Surgical resection is performed for symptomatic cases.