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KEY FACTS

Terminology
- Rare, benign, locally aggressive, nonencapsulated mesenchymal neoplasms of connective or fibrous tissue
Imaging
- Can be intraabdominal (particularly small bowel mesentery) or extraabdominal (including abdominal wall) - When involving abdominal wall, often involve rectus or oblique muscles, frequently at incision sites
- Usually solid with well-defined margins, but can also be infiltrative in appearance
- Classically thought to be low signal on all MR pulse sequences due to fibrous content, but this is unreliable
- Usually hyperdense to muscle on NECT and hypoenhancing on CECT (but rarely avidly enhancing)
Pathology
- Strong associations with Gardner syndrome and familial adenomatous polyposis (FAP)
- Other major risk factors include previous abdominal surgery (75% of cases), trauma, pregnancy, or oral contraceptives
Clinical Issues
- Complications arise from locally aggressive growth with involvement of adjacent structures, such as small bowel obstruction, ureteral obstruction, bladder outlet obstruction, hydrosalpinx, etc.
- Surgical resection was once mainstay of treatment, but this has now become increasingly controversial due to morbidity and mortality of resection, as well as high risk of recurrence (even in setting of R0 resection)
- Active surveillance now mainstay of treatment whenever possible (particularly when lesions are small and asymptomatic), as many lesions remain stable or even spontaneously regress
- Conservative management with variety of pharmacologic agents and radiation treatment increasingly utilized even for symptomatic lesions

TERMINOLOGY

Synonyms
- Deep or aggressive fibromatosis
Definitions
- Rare, benign, locally aggressive, nonencapsulated mesenchymal neoplasms of connective or fibrous tissue

IMAGING

General Features
- Best diagnostic clue
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- Small bowel mesentery or abdominal wall mass arising at site of scarring from prior surgery
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- Location
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- Can be intraabdominal or extraabdominal (including abdominal wall)
        - **Abdominal desmoids**
                  - Account for 2/3 of all desmoid tumors
                  - Tumors associated with Gardner syndrome or familial adenomatous polyposis (FAP) are usually intraabdominal
                  - Most commonly occur in small bowel mesentery but can occur nearly anywhere
        - **Extraabdominal**
                  - Pregnancy-related desmoid tumors tend to occur within abdominal wall
                  - 1/3 occur in shoulder and upper extremity
                  - ~ 20% in chest wall, ~ 10% in head and neck
                  - Musculature most often involved: Rectus, internal/external oblique, psoas, pelvic (rare)
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- Morphology
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- Most often demonstrate clear, lobulated margins on imaging (75%), but minority of cases can appear ill defined and infiltrative (25%)
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- Key concepts - Locally aggressive primary mesenchymal tumor - Sometimes classified as low-grade fibrosarcoma or subgroup of fibromatosis - Tend to arise in musculoaponeurotic planes - Tend to invade locally, recur after treatment, and grow very rapidly, especially in Gardner syndrome - May involve bowel loops, bladder, ribs, pelvic bones, and virtually any other structure - Lesions are locally aggressive and cause morbidity/mortality primarily due to local invasion, but do not metastasize - Desmoids can be solitary or multiple (15% of cases) - Etiology - Most cases are sporadic - 75% of patients with desmoid tumors have had prior abdominal surgery - May be associated with Gardner syndrome and FAP, which can be characterized by a number of abnormalities - Familial polyposis coli, osteomas, dental defects, congenital pigmented lesions of retina - Epidermoid (sebaceous) cyst and fibromas of skin - Periampullary, adrenal, thyroid, and liver malignancies - 18-20% of patients with Gardner syndrome develop desmoids and desmoids account for 45% of fibrous lesions in Gardner syndrome
CT Findings
- Abdominal wall desmoids - Usually solid with well-defined margins (but can be infiltrative in appearance) - Usually hyperdense compared to surrounding muscle on NECT - Usually hypoenhancing on CECT, but can in some cases be quite avidly enhancing - Often involve rectus or oblique muscles and occur frequently at incision sites
- Mesenteric desmoids - Soft tissue mass with well-defined or ill-defined margins - Hyperdense relative to muscle on NECT with variable, heterogeneous enhancement on CECT - Whorled appearance: Radiating fibrotic strands into adjacent mesenteric fat - May displace, retract, or compress adjacent bowel loops and potentially cause small bowel obstruction - Can infiltrate into adjacent organs and musculature - Calcification very uncommon
MR Findings
- Can be poorly marginated or very well circumscribed - Often will cross fascial boundaries (1/3 of cases) and may be lobulated or infiltrative
- Classically thought to be low signal on all pulse sequences due to fibrous content - Not consistent or common feature, and may be seen with other entities (including malignancies, such as fibrosarcoma and malignant fibrous histiocytoma) - Usually homogeneously isointense or mildly hypointense on T1WI - Can demonstrate T2 hypointensity due to fibrotic component, but in practice more often heterogeneously high signal on T2WI - Higher T2 signal more common with actively growing or aggressive desmoids - Internal bands of low signal on all pulse sequences (corresponding to fibrosis and collagen) in 2/3 of cases - Variable enhancement on post gadolinium sequences, but usually heterogeneous
- No specific MR features to differentiate desmoids from malignancy or to make specific imaging diagnosis
Ultrasonographic Findings
- Well-defined mesenteric mass with variable echogenicity
Radiographic Findings
- Fluoroscopic double-contrast studies - FAP: Innumerable, variably sized radiolucent filling defects in colon
Imaging Recommendations
- Best imaging tool
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- Multiplanar CT or MR
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DIFFERENTIAL DIAGNOSIS

Soft Tissue Sarcoma
- Imaging cannot differentiate desmoid tumor in abdominal wall or musculature from sarcoma and biopsy ultimately required to make this distinction
- History of prior surgical incision at site of mass raises possibility of desmoid rather than malignancy
Leukemia and Lymphoma
- Retroperitoneal and mesenteric lymphadenopathy, which is typically much softer than desmoid (envelops, but rarely obstructs, bowel or vessels)
Omental or Mesenteric Metastases
- Usually multiple less well-defined lesions that are often associated with stranding and induration in mesentery and omentum
Carcinoid Tumor
- Usually occurs in right lower quadrant ileocolic mesentery
- Desmoplastic reaction and calcification very common, features which are not typically found in desmoids
Small Bowel Tumors Extending Into Mesentery
- Gastrointestinal stromal tumors (GISTs) or small bowel adenocarcinoma can extend into mesentery and appear similar to desmoid tumor
Abdominal Mesothelioma
- Arises from serosal lining of pleural and peritoneal cavity
- Mostly affects males exposed to asbestos
- Peritoneal cavity is involved alone or in association with pleural disease
- Usually diffusely thickens omentum and mesentery ± peritoneal and omental nodular masses, ascites
Sclerosing Mesenteritis
- Usually less mass-like than desmoid, although retractile mesenteritis can produce discrete mesenteric mass with desmoplastic reaction and calcification

PATHOLOGY

General Features

Etiology

- Exact cause is unknown
- Majority of cases are sporadic
- Strong associations with Gardner syndrome and FAP
        - Due to mutation in *APC* gene (5q22)
        - Autosomal dominant disorder characterized by innumerable colonic polyps and multiple extracolonic tumors (including desmoids in 18-20% of cases)
- Other risk factors include previous abdominal surgery (75% of cases), trauma, pregnancy, or oral contraceptives
- Most often in women of childbearing age

Staging, Grading, & Classification
- Church et al staging system for desmoid tumors (primarily intended for FAP-related desmoids) - Stage I: Asymptomatic patients with tumors < 10 cm that are not growing - Stage II: Mildly symptomatic patients with tumors < 10 cm that are not growing - Stage III: Moderately symptomatic, bowel/ureter obstruction, tumors 10-20 cm, or tumor slowly growing - Stage IV: Severely symptomatic, septic complications (such as abscess/fistula), tumor > 20 cm, or tumor rapidly growing - Staging system can be used to guide treatment, with stage I and II desmoids potentially treated with active surveillance (along with low toxicity drugs), while stage III and IV desmoids often treated with surgical resection and more aggressive pharmacologic treatment
Gross Pathologic & Surgical Features
- Desmoid tumors may be intermediate step between reparative process and true malignancy
- Tan/white, firm, well- or poorly defined mass
- May be "rock hard" and resistant to percutaneous biopsy
Microscopic Features
- Well-differentiated fibroblasts invading surrounding tissues
- Elongated spindle-shaped cells of uniform appearance with dense bands of collagen

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Patients may be asymptomatic or may present with abdominal pain and palpable mass
- Acute abdominal findings
        - Due to ischemia/ulceration of mass
        - Encasement of mesentery and bowel → ischemia and obstruction → progressive resection of bowel → short gut syndrome
        - Hydronephrosis due to ureteral encasement

Demographics

Age

- 70% of cases between 20-40 years old
- Tends to be more aggressive in younger patients

Sex

- M:F = 1:3
- Increased incidence in women of childbearing age

Epidemiology

- Rare: 2-4 cases per million per year
- 18-20% of patients with Gardner syndrome develop desmoid tumor
        - Mesenteric location more common than abdominal wall desmoid
- 8-18% of desmoids are related to pregnancy, typically develop in 3rd trimester or post partum, and are most often located in abdominal wall

Natural History & Prognosis
- Complications - Locally aggressive growth pattern with compression and invasion of adjacent structures - Intraabdominal desmoids tend to be most aggressive and infiltrative (particularly when associated with FAP or Gardner syndrome) - Can cause bowel obstruction, ureteral obstruction, and bowel ischemia due to vasculature encasement - In pelvis, can cause bladder outlet obstruction or involve fallopian tubes and cause hydrosalpinx - Extraabdominal desmoids can involve nerves and cause pain - Chest wall desmoids can invade pleura - Short gut syndrome can be major issue after multiple small bowel resections - High recurrence rate (up to 2/3 of cases) - Imaging and pathology not predictive of recurrence
- Poor prognostic features - Large size of tumor ( > 10 cm) and multiplicity - Extensive involvement of bowel loops, encasement of mesenteric vessels, and involvement of ureters
Treatment
- Active surveillance now considered 1st-line treatment whenever possible, and National Comprehensive Cancer Network (NCCN) now recommends that most patients should be initially placed on active surveillance in absence of progressive or symptomatic disease - Bonvalot et al found that of those tumors assigned to active surveillance 1/3 remained stable and 1/3 actually spontaneously regressed
- While surgical treatment was once mainstay of desmoid treatment, this has now increasingly become controversial as result of morbidity and mortality associated with resection (although surgery may still be necessary in some cases) - May be difficult due to involvement of adjacent critical structures - Particularly when small bowel mesentery involved, surgery can result in significant morbidity (bowel ischemia, short gut syndrome, obstruction, etc.) - Small bowel transplantation may be option in patients who require resection for intraabdominal desmoid and undergo significant bowel resection - Recurrence after surgery is very common, particularly with extraabdominal desmoids, even if surgical margins are negative - Exact relationship between negative margins and local recurrence is unclear based on several studies, which is why performing resections that prioritize maintaining local function may be more important than simply trying to achieve R0 resection - Recurrence rates for desmoids is roughly 50% and may be higher for intraabdominal desmoids (57-88%) - FAP and larger tumor size (> 10 cm) increases risk of recurrence
- Conservative management now increasingly utilized for even symptomatic desmoids (in lieu of surgery) - Systemic therapy: Cytotoxic agents (including anthracyclines), antiestrogen agents (e.g., tamoxifen), interferon, molecular-targeted agents (e.g., imatinib), steroids, NSAIDs (e.g., sulindac) - Radiation therapy: Can be effective for establishing local control of tumor, but usually utilized after other options exhausted due to toxicity

DIAGNOSTIC CHECKLIST

Consider
- Consider desmoid tumors in patients with history of prior abdominal surgery
- Look for other features of Gardner syndrome
- Rule out other more common causes of solid mesenteric mass
Image Interpretation Pearls
- Soft tissue density mesenteric mass ± invasion, displacement, or encasement of bowel loops and vessels

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References

Selected References

Images

Selected Images

Axial CECT demonstrates a large, homogeneous mass in the deep pelvis involving the rectosigmoid colon and portions of the small bowel. While this was prospectively thought to perhaps be a gastrointestinal stromal tumor on imaging, it turned out to be a desmoid tumor at resection.

Axial CECT demonstrates a homogeneous mass in the right psoas muscle that was incidentally discovered on imaging done for other reasons. This was shown to be a desmoid tumor on biopsy.

Sagittal T2 MR demonstrates a relatively T2-hypointense mass in the subcutaneous soft tissues of the posterior pelvic wall in a patient who had felt this mass growing over time.

Axial T1 C+ FS MR in the same patient demonstrates that the mass exhibits substantial enhancement with mildly irregular margins . This was found to be a desmoid tumor at resection.

Axial CECT demonstrates a homogeneously enhancing mass in the right hemipelvis.

Axial CECT in the same patient demonstrates a large avidly enhancing mass in the right lower quadrant. This was a patient with familial adenomatous polyposis (FAP), and both of these lesions were found to represent desmoid tumors.

Axial CECT shows a large mesenteric desmoid with involvement of multiple bowel loops that had been slowly growing on serial examinations. The patient underwent surgical resection, but desmoids with extensive bowel involvement can often be very difficult to resect.

Axial CECT demonstrates a well- circumscribed, homogenous mass in the pelvis involving the colon and small bowel, found to be a desmoid tumor at resection.

Coronal T2 HASTE MR in a patient who had undergone bowel resection roughly 6 months earlier demonstrates a well-circumscribed, T2-hypointense mass in very close proximity to the surgical site.

Axial T1 C+ MR in the same patient demonstrates that the mass demonstrates homogeneous enhancement, which increases on this delayed phase image. Because of their fibrotic component, desmoids can demonstrate relative T2 hypointensity and increasing delayed enhancement, as in this case.

Additional Images

Axial CECT in a 36-year-old man 12 months following a colectomy for Gardner syndrome shows a solid mesenteric desmoid .

Axial CECT 20 months following a colectomy for Gardner syndrome shows rapid growth of a mesenteric mass (desmoid tumor).

Axial CECT shows desmoid in the subcutaneous tissue adjacent to a scar from a prior paramedian incision.

Axial CECT shows multiple omental masses near the site of prior colon surgery, representing desmoid tumors. Note the surgical clip .

Axial CECT in a patient with Gardner syndrome shows a large, bilobed, mesenteric desmoid tumor.

Axial NECT in a patient with Gardner syndrome shows desmoid tumors filling the abdomen, obstructing kidneys and deforming the abdominal wall.

Axial CECT in a 79-year-old woman shows a homogeneous omental mass . This was a sporadic form of desmoid.

Axial NECT in a 79-year-old woman shows a homogeneous, enhancing mass in the left pelvis. CT-guided biopsy showed a "rock hard" mass but enough tissue to confirm desmoid tumor.

Axial CECT demonstrates a very well-circumscribed, relatively hypoenhancing mass in the right anterior abdominal wall musculature in a patient with a prior history of a surgical incision in this location, representing a desmoid tumor.

Axial CECT demonstrates a hypodense soft tissue mass in the left mesentery in close proximity to the jejunum, stomach, and pancreas. There is a some surrounding fat stranding and inflammatory change.

Axial T2 FS MR in the same patient demonstrates that the mass has both cystic and solid components. This was originally thought to possibly represent a jejunal gastrointestinal stromal tumor, but was found to be a sporadic desmoid in a patient without risk factors.

Axial CT reveals a solid mass that involves the lower rectus muscle. This is a surgically proven desmoid tumor. In Gardner syndrome, desmoids may involve the mesentery or abdominal wall. As with other types of fibrous masses, such as keloids, sites of prior surgery or trauma are commonly involved.

Axial CT in the same patient again reveals a solid mass that involves the lower rectus muscle. This was a surgically proven desmoid tumor. In Gardner syndrome, desmoids may involve the mesentery or abdominal wall. As with other types of fibrous masses, such as keloids, sites of prior surgery or trauma are commonly involved.

Axial CECT shows an isolated mesenteric desmoid in a 24-year-old woman with no personal evidence of colonic polyps but a family history of familial polyposis. Note the infiltrative mesenteric mass .

Axial CECT in a 75-year-old Black woman shows an isolated mesenteric desmoid as a nonspecific soft tissue density mass adjacent to the bladder , uterus, and colon. A core needle biopsy was requested. The mass was extremely hard and bent each of the biopsy needles.

Axial CECT demonstrates a soft tissue mass in the left upper quadrant with surrounding soft tissue edema and induration, found to represent a desmoid at resection.

Axial CECT demonstrates a very homogeneous, hypoenhancing mass in the pelvis encasing loops of adjacent bowel. This was found to be a desmoid tumor. Desmoids with extensive involvement of the bowel can be very difficult to surgically resect.

Axial CECT demonstrates a relatively homogeneous, enhancing, well-circumscribed mass in the right anterior pelvis.

Axial CECT in the same patient demonstrates a very similar-appearing smaller mass in the more inferior pelvis. This was a patient with Gardner syndrome, and both of these lesions were found to represent desmoid tumors.

Axial T1WI C+ FS MR in the same patient demonstrates relatively avid enhancement of the mass , which is once again noted to be quite infiltrative and poorly marginated. In cases like this, only histologic confirmation can differentiate a desmoid from a soft tissue malignancy.

Axial CECT demonstrates an infiltrative, hypoenhancing mass in the right anterior abdominal wall musculature at the site of a prior surgical incision.

Axial CECT in a young woman with Gardner syndrome 2 years after total colectomy shows mesenteric fibromatosis (desmoids) encasing the entire small bowel mesentery, filling the abdominal cavity.

39 KiB Raw Blame History

KEY FACTS

Terminology

Imaging

Pathology

Clinical Issues

TERMINOLOGY

Synonyms

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Morphology

CT Findings

MR Findings

Ultrasonographic Findings

Radiographic Findings

Imaging Recommendations

Best imaging tool

DIFFERENTIAL DIAGNOSIS

Soft Tissue Sarcoma

Small Bowel Tumors Extending Into Mesentery

PATHOLOGY

General Features

Etiology

Staging, Grading, & Classification

Gross Pathologic & Surgical Features

Microscopic Features

CLINICAL ISSUES

Presentation

Most common signs/symptoms

Demographics

Age

Sex

Epidemiology

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Consider

Image Interpretation Pearls

References

Selected References

Images

Selected Images

Additional Images

39 KiB

Raw Blame History