Mesenteric desmoid tumor (deep fibromatosis) is a fibroblastic neoplasm arising from mesenteric fat and connective tissue, locally aggressive but non-metastasizing. Strongly associated with familial adenomatous polyposis (FAP) and Gardner syndrome — develops in 10-20% of FAP patients. Sporadic form is rarer and usually occurs after previous abdominal surgery or trauma. The tumor can encase mesenteric vessels causing intestinal ischemia and ureters causing hydronephrosis. Histologically composed of monotypic fibroblasts with characteristic beta-catenin mutation. On CT, appears as a well-defined or infiltrative soft tissue mass in the mesentery; on MRI, T2 signal intensity varies with tumor cellularity and collagen content. Treatment is multidisciplinary — observation, pharmacological (sulindac, tamoxifen, sorafenib) or surgical options exist.
Age Range
15-55
Peak Age
35
Gender
Equal
Prevalence
Rare
Desmoid tumors arise from myofibroblast/fibroblast proliferation. Constitutive activation of the Wnt/beta-catenin signaling pathway plays a central role in pathogenesis — CTNNB1 gene mutation (sporadic) or APC gene mutation (FAP-associated) increases beta-catenin accumulation and target gene (MYC, cyclin D1) transcription → uncontrolled fibroblast proliferation. In FAP patients, abdominal surgical trauma after colectomy may trigger desmoid development. The tumor grows slowly but infiltrates and encases surrounding structures — particularly encasing SMA/SMV causing intestinal ischemia, encasing ureters causing obstructive uropathy. Histologically, spindle-shaped fibroblasts are arranged within collagen stroma — the collagen-cell ratio determines MRI signal characteristics: cell-dominant → T2 hyperintense, collagen-dominant → T2 hypointense.
Desmoid tumor encasing mesenteric vessels without invasion — vessel lumen remains patent while mass completely surrounds the vessel. This pattern is characteristic for desmoid tumor and a critical finding affecting surgical decision.
Well-defined or infiltrative, homogeneously or heterogeneously enhancing soft tissue mass in the mesentery on portal venous phase. Density is generally close to muscle density (30-50 HU non-contrast) with moderate to prominent enhancement in contrast phase. Mass size can range from a few cm to 20+ cm. Mesenteric vessels may be encased by the mass but generally remain patent (encasement rather than invasion).
Report Sentence
Soft tissue mass in the mesentery is observed, consistent with mesenteric desmoid tumor (deep fibromatosis).
Variable signal intensity on T2-weighted images — cellular-dominant areas show high signal, collagen-dominant areas show low signal. This heterogeneous T2 signal pattern is characteristic for desmoid. Band-like T2 hypointense areas (collagen bands) may be seen within the tumor. Cellular/collagen ratio reflects treatment response and tumor biology.
Report Sentence
Heterogeneous T2 signal (hyper and hypointense areas) in the mesenteric mass on MRI is observed, consistent with desmoid tumor.
Encasement of SMA/SMV and branches by the mass on arterial phase — vessels pass through the mass but generally remain patent. Vessel wall irregularity or occlusion is rare. This 'encasement' pattern is the characteristic growth pattern of desmoid tumor and is critically important for surgical planning.
Report Sentence
The mesenteric mass encases SMA/SMV branches with patent vessel lumens; this pattern is consistent with desmoid tumor.
Variable diffusion pattern on DWI — cellular-dominant areas show mild to moderate diffusion restriction, collagen-dominant areas show no restriction. ADC values are heterogeneous (1.0-1.8 × 10⁻³ mm²/s). This pattern may change after treatment — if cellularity decreases with treatment, ADC increases.
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Heterogeneous diffusion pattern in the mesenteric mass on MRI is observed, consistent with mixed cellularity and collagen content of desmoid tumor.
Increasing enhancement in the tumor on delayed phase — progressive enhancement pattern. Fibrous tissue slowly absorbs contrast agent and reaches peak enhancement in late phase. This pattern shows similarity with lymphoma (early enhancement, rapid washout) and carcinoid desmoplasia but clinical context (FAP history) aids differentiation.
Report Sentence
Increasing enhancement in the mesenteric mass on delayed phase (progressive pattern) is observed, consistent with fibrous tissue-dominant mass.
Hypoechoic or mixed echogenicity solid mass in the mesentery on B-mode ultrasound. Internal structure may be homogeneous or heterogeneous — hypoechoic cellular areas and hyperechoic fibrous bands may coexist. Moderate vascularity on Doppler. US can be used for initial detection and follow-up of desmoid but does not provide as detailed evaluation as CT/MRI.
Report Sentence
Mixed echogenicity solid mass in the mesentery on ultrasound is observed, consistent with desmoid tumor.
Criteria
Desmoid developing in FAP/Gardner syndrome background — APC gene mutation
Distinct Features
Generally develops after colectomy. May be multifocal. Prognosis more complex — recurrent course common. Genetic counseling recommended.
Criteria
Desmoid without FAP association — CTNNB1 gene mutation (beta-catenin)
Distinct Features
Generally in young women. Previous surgery or trauma may be triggering. Solitary lesion predominant. Spontaneous regression has been reported in some cases.
Criteria
Rapid growth, vascular encasement and obstruction findings
Distinct Features
High risk of mesenteric ischemia. T2 hyperintense dominant on MRI (cellular). Requires active treatment — surgery or systemic therapy.
Distinguishing Feature
In carcinoid, sunburst calcification and ileal primary tumor; in desmoid, calcification rare and no intestinal primary lesion
Distinguishing Feature
In lymphoma, homogeneous T2 hyperintense signal and homogeneous DWI restriction; in desmoid, heterogeneous T2 signal (hyper + hypointense areas)
Distinguishing Feature
GIST shows exophytic growth from bowel wall; desmoid develops in the mesentery independently of bowel wall
Distinguishing Feature
In metastasis, known primary malignancy and usually multiple lesions; desmoid is solitary with FAP history and does not metastasize
Urgency
routineManagement
medicalBiopsy
NeededFollow-up
3-monthTreatment approach for mesenteric desmoid tumor is determined by tumor behavior. Active observation (MR follow-up every 3-6 months) is preferred for asymptomatic, stable desmoids. Pharmacological therapy (sulindac + tamoxifen, sorafenib, DOX/VBL chemotherapy) is applied for symptomatic or growing tumors. Surgical resection is considered as last resort due to high recurrence rate (40-60%) — surgical morbidity is high especially with vascular encasement. Genetic counseling and family screening recommended for FAP patients. MRI preferred over CT for monitoring treatment response and progression.
Desmoid tumor is locally aggressive and may encase ureter, bowel, and vascular structures. Treatment options include surgery, pharmacotherapy (sulindac, tamoxifen), and surveillance. Genetic counseling should be provided for FAP patients.