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Mesenteric fibromatosis (also called intra-abdominal desmoid tumor) is a rare, benign but locally aggressive fibroblastic proliferation arising from the mesenteric connective tissue. Although non-metastasizing, it shows infiltrative growth and a high tendency for local recurrence.

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Etiopathogenesis

Origin: fibroblasts/myofibroblasts of mesenteric connective tissue.
Associations:
- Familial adenomatous polyposis (FAP), especially Gardner syndrome.
- Previous abdominal surgery or trauma.
- Hormonal factors (estrogen sensitivity reported).
Pathology: infiltrative spindle-cell proliferation within collagen matrix.

Clinical Features

Most often affects young adults (20–40 years), slight female predominance.
Presentations:
- Abdominal mass (slow-growing, firm, deep).
- Pain, discomfort, bloating.
- Obstruction of bowel or ureter if encasing loops/ureters.
- May mimic malignancy due to infiltrative growth.

Radiology

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CT/MRI show an infiltrative mesenteric mass encasing vessels/loops.

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Modality	Imaging features
US	Hypoechoic, ill-defined intra-abdominal/mesenteric mass.
CT	• Well-defined but infiltrative soft-tissue mass in mesentery.
• Homogeneous attenuation (iso- to slightly hyperdense vs muscle).
• Variable enhancement: mild to moderate, progressive.
• May encase bowel loops and vessels without causing obstruction (distinguishes from lymphoma which encases but is homogeneous).
• Can cause kinking/narrowing of small bowel → obstruction.
MR	• T1: Iso- to hypointense to muscle.
• T2: Variable – may be hypointense due to collagen (mature lesions), or hyperintense in cellular/edematous lesions.
• Post-contrast: moderate heterogeneous enhancement.
• Helps assess relation to vessels and bowel, and follow-up.
PET-CT	Generally low to moderate FDG uptake (less than high-grade sarcomas or lymphoma).

Differentials

Mesenteric lymphoma: bulky, homogeneous, sandwich sign; does not usually obstruct.
Gastrointestinal stromal tumor (GIST): arises from bowel wall, exophytic; more heterogeneous, enhancing.
Carcinoid mesenteric mass: spiculated with desmoplastic reaction, calcification, bowel tethering.
Metastatic deposits: multiple, variable appearance.