Desmoid tumors are benign, non-inflammatory fibroblastic tumors with a tendency for local invasion and recurrence post resection. They are sometimes considered a locally aggressive proliferative disease within the family of soft-tissue sarcomas but, metastasis is uncommon ^7,11. 

Terminology

The terms desmoid tumor and aggressive fibromatosis are occasionally used synonymously by some authors ⁹. This article will focus on the abdominal presentation of this fibroblastic tumor. For the musculoskeletal presentation, please refer to the latter.

Epidemiology

They are rare tumors, thought to account for only ~0.03% of all neoplasms ⁶. Desmoid tumors are found in all age groups but are most frequently encountered between 20 and 40 years of age. They are seen more in women (2:1). They are rare lesions with an estimated incidence of 3.7 new cases per million population per year ¹.

Associations

• some cases have been associated with pregnancy and estrogen therapy ¹⁰

• Gardner syndrome

• in the case of mesenteric desmoid they are seen either sporadically or in association with familial polyposis coli syndrome (FAP): 9-18% of FAP cases may have a desmoid tumor ⁸

Clinical presentation

Desmoid tumors present as masses, and as such presentation depends on location.

Pathology

Their exact etiology remains uncertain, although they are frequently associated with previous trauma or surgical incision. On the molecular level, desmoids are characterized by mutations in the β-catenin gene, CTNNB1, or the adenomatous polyposis coli (APC) gene ⁷.

Location

Frequent locations in the abdomen are the abdominal wall, the root of the mesentery and the retroperitoneum.

Classification

Desmoid-type fibromatosis is listed in the WHO classification of soft tissue tumors under the category "fibroblastic/myofibroblastic tumors".

Radiographic features

Ultrasound

Desmoid tumors are the commonest neoplasms of the abdominal wall and typically appear as homogeneously hypoechoic masses. They may have a similar appearance to muscle, may be lobulated and may show vascularity on color Doppler interrogation.

CT

• most desmoid tumors are well-circumscribed masses, although in some cases they may appear more aggressive with ill-defined margins

• most are relatively homogeneously or focally hyperattenuating when compared to soft tissue on the non-contrast scan

• most will demonstrate enhancement following administration of intravenous contrast

MRI

MRI, as is the case with other soft tissue tumors, is more sensitive to local tumor extension. Their appearance is accounted for by their dense cellularity. Typical signal characteristics include:

• T1: low signal intensity

• T2: low signal intensity

• T1 C+ (Gd): may show homogeneous, inhomogeneous, or no significant enhancement ⁸

Treatment and prognosis

Most cases can have relatively good prognosis and watchful waiting is now considered a reasonable option in selected asymptomatic patients ⁷. Other management options include ^ref:

• surgical resection (traditionally used, although recurrence rate is high)

  • NSAIDs and anti-estrogens can be used to reduce the rate of recurrence

• radiation therapy

Differential diagnosis

• small bowel neuroendocrine tumor ^ref

• sclerosing mesenteritis: tends to be more central at the "root" of the mesentery ^ref

History and etymology

The term "desmoid" originates from the Greek word "desmos" (Δεσμός’) meaning band or tendon-like.

See also

• desmoplastic fibroma

• Gardner fibroma