Diffuse Infiltration Fibrosis/Desmoid

Diffuse extraperitoneal fibrosis, also known as retroperitoneal fibromatosis, desmoid tumor, and Ormond’s disease, is a locally invasive but benign chronic condition. Extraperitoneal fibrosis is idiopathic in about two thirds of patients. Some evidence suggests an underlying autoimmune response manifesting as a vasculitis and fibrosis. Both mesenteric and extraperitoneal fibromatosis (fibrosis) present most often as a discrete desmoid tumor; a diffuse infiltrate is less common. Fibrous tissue is noncapsulated, poorly marginated, and infiltrates surrounding structures. Its relationship to sclerosing peritonitis and mesenteritis is conjecture. Indeed, some of the patients discussed previously (see Sclerosing Peritonitis/Mesenteritis) probably should be included here (and vice versa).
Etiology Secondary forms of fibromatosis/desmoid are associated with both malignant and benign disorders. It develops in response to some infiltrating malignancies, and at times the term malignant retroperitoneal fibrosis is used to describe a reactive fibrosis secondary to such neoplastic infiltration; malignant cells tend to be scattered throughout the fibrosis. A distinction between malignant and nonmalignant retroperitoneal fibrosis is of obvious clinical importance and thus an extensive biopsy is often indicated.
An association with methysergide and ergotamine use appears to be greater than by chance. Extraperitoneal fibrosis has been reported following treatment of Parkinson’s disease with Ldopa analogues; a number of these patients have underlying atherosclerosis and it is difficult to put the relationship among atherosclerosis, drug therapy, and the subsequent development of fibrosis into proper perspective.
A rare patient develops extraperitoneal fibrosis secondary to actinomycosis and other chronic infection. Extensive extraperitoneal fibrosis develops as a reaction to some foreign bodies. Thus fibrosis is induced by extravasated barium during bowel perforation; similar to some of the other reactive fibroses mentioned above, such fibrosis is a local reaction surrounding the barium crystals and is not associated with fibrosis at other sites. Desmoid tumors are common in familial adenomatous polyposis. In fact, this polyposis syndrome should be suspected in a patient with a newly discovered rectus abdominis muscle desmoid tumor.
Prior abdominal surgery increases the risk for desmoids; in an occasional patient desmoids begin to develop in trocar sites within months after laparoscopy.Less often a desmoid develops in a patient without familial polyposis and at a site unrelated to prior surgery. These sporadic desmoids are less likely to recur after resection than familial ones. A mesenteric desmoid tumor can develop after radiation therapy. These patients often also develop leg edema and protein-losing enteropathy due to intestinal lymphangiectasia.
Classification of desmoplastic fibroblastomas (collagenous fibroma) is not clear. One slowly growing heterogeneous tumor was hypointense on T1-weighted images, mixed hypo- and hyperintense on T2-weighted images and showed heterogeneous contrast enhancement; the hypointense regions consisted mostly of collagen.
image
Rectus sheath desmoid tumor (arrow). clinical Extraperitoneal fibrosis usually involves structures from the renal hila inferiorly.A somewhat atypical variant is to find fibrosis limited to the pelvis. Although benign, desmoids invade locally and have a high potential for recurrence.
Complications of desmoid tumors account for part of the mortality associated with familial adenomatous polyposis. Symptoms result from the gradual compression of adjacent structures, including ureters, retroperitoneal vessels and nerves, and portions of the gastrointestinal tract. Extraperitoneal
fibrosis encasing the ureters results in hydronephrosis, at times unilateral. The ureters are displaced medially. Once a diagnosis of extraperitoneal fibrosis is established, in a setting of hydronephrosis, ureteral decompression is necessary to save the kidney. Laparoscopic ureterolysis is feasible, although often in vain. Placement of double-J ureteric stents is helpful on a temporary basis. With time, soft polyurethane stents tend to become obstructed due to continued extrinsic ureteral compression, and they need to be replaced with more rigid ones.
Occasionally extraperitoneal fibrosis involves the bile ducts and leads to obstructive jaundice; imaging findings can suggest extrahepatic sclerosing
cholangitis or a pancreatic malignancy.
At times fibrosis leads to both hydronephrosis and biliary obstruction. Abscesses can develop within a desmoid tumor, at times communicating to the bowel. Some of these abscesses can be managed initially with percutaneous abscess drainage. Extraperitoneal fibrosis tends to respond to
steroid therapy. Immunosuppressive therapy has also achieved some success. Surgical therapy is difficult due to the often-diffuse infiltration. Also, surgery often tends to exasperate recurrence. Once the diagnosis is established,
follow-up is by CT or US. Some unresectable desmoid tumors regress after
being treated with radiation therapy. The role of hyperthermia is not clear. Spontaneous regression of extraperitoneal fibrosis has also been reported, albeit rarely.
Both growth and response to therapy of a desmoid are readily evaluated with imaging. Iliac vein and inferior vena caval stenosis secondary to extraperitoneal fibrosis is often approached surgically but can be treated by
venous thrombectomy and bilateral iliac stenting, but keep in mind the often temporary nature of such therapy.
Imaging Most desmoids develop in the mesentery and abdominal wall, with only an occasional one being extraperitoneal in location. A rare one involves both extra- and intraperitoneal structures.
In some patients a specific site of origin cannot be determined. Although at times imaging suggests the diagnosis, no specific finding is pathognomonic.
Imaging identifies a desmoid either as a discrete tumor or a poorly marginated infiltration.With diffuse extraperitoneal infiltration, the first task
is to establish that the diagnosis is indeed fibrosis rather than an underlying malignancy. Rather than being displaced, adjacent vessels and bowel become encased. Imaging cannot differentiate primary benign fibromatosis from a secondary one due to malignant infiltration, although malignancies increase in size faster than a benign infiltration. Extraperitoneal fibrosis is usually diffuse, but occasionally is well marginated or even nodular.Contour irregularities are not a reliable differential. Either extensive percutaneous biopsies or surgical exploration is often necessary. Negative percutaneous
biopsies should be interpreted with caution.
Precontrast CT of most extraperitoneal fibrosis shows a density similar to that of adjacent muscle or is even slightly hyperdense. The tissue tends to enhance postcontrast and may appear somewhat hyperdense. At times the
appearance mimics that of a diffuse tumor. Magnetic resonance imaging of diffuse fibrosis and desmoids usually reveals hypointense signals on both T1- and T2-weighted images. An occasional complex infiltrating tumor exhibits iso- or even hyperintense signal
intensities on T2-weighted images. Postcontrast enhancement is variable.
Desmoids and retroperitoneal fibrosis show Ga-67-citrate uptake. Some correlation exists among clinical symptoms, disease activity, and Ga 67 scintigraphic activity.
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