eP308 - A Hidden Challenge: Rare Desmoid Mesenteric Tumor Causing Internal Hernia and Small Bowel Obstruction in a Virgin Abdomen

Purpose/Background: Desmoid tumors is a rare tumor and accounts for 2-4 per million population and 0.03% of all tumors with peak incidence around 30-40 years of age. Most desmoid tumors occur sporadically most commonly due to mutation in the beta-catenin pathway however, about 15% of the cases are associated with syndromes like FAP or Gardener’s syndrome. It usually arises from spindle cells that resemble myofibroblasts in a collagenous stroma.
Desmoid tumors are known for the aggressive local invasiveness, with rare metastasis. The pathogenesis is not clearly understood since most of the cases are sporadic. No significant contributing factors have been clearly inked to its occurrence but hormonal, genetic and traumatic factors have been shown to have some effect on its incidence.Methods/Interventions: A 61-year-old Caucasian male with a history of polymyositis (on Methotrexate), hypothyroidism but no significant surgical history. He presented to the emergency room with abdominal pain, recurrent nausea and vomiting as well as decreased oral intake for the preceding week. Computed tomography imaging showed dilation of the small bowel with wall thickening and infiltration of adjacent mesenteric fat and distension of mesenteric veins with overall findings raising concern for small bowel obstruction secondary to internal hernia.Results/Outcomes: A diagnostic laparoscopy was first attempted but failed due to dense adherence of multiple segments of small bowel and transverse colon to a deep mesenteric structure. Case was converted to open laparotomy where the small bowel was run distally from fold of Treves towards proximal direction where multiple segments of small bowel as well as the transverse colon were densely adhered to a thickened mesenteric sheet that looked grossly abnormal. Careful, blunt lysis of adhesion was carried during which an internal hernia was found containing small bowel and reduced. The thickened mesenteric sheet was found to be wide spanning and originating from the root of the mesentery which made it impossible to obtain a complete surgical resection since it was not a discrete mass. The sheet was then biopsied, and the abdomen was closed after freeing all the small and large bowel.
The patient did well clinically post operatively and was discharged after return of bowel function and tolerating oral intake. Biopsy results came back showing mesenteric desmoid fibromatosis.Conclusion/

Discussion: The goal of treatment of desmoid tumors is local control however, based on the location, that may not be possible in some cases. In the case of our patient, due to its wide spanning and origin from the root of the mesentery, it was not possible to resect it at the time of his surgical intervention. The presentation was also unique since it was a thickened mesenteric sheet and not a discrete mass.
Several non-operative treatments including radiation and medications have been proposed for desmoid tumors. Radiation has been shown to be beneficial for those who have unresectable masses or unable to get an R0 resection. Medical treatments including chemotherapy (doxorubicin or vinca alkaloids-based agents), Tyrosine kinase inhibitors, hormonal agents (for cases that occur during pregnancy) as well as NSAIDs have also been shown to have significant benefits.
To conclude, mesenteric desmoid tumors represent a hidden challenge due to their critical location with many factors that can affect their treatment plan."Coronal CT findings of small bowel obstruction and mesenteric fat infiltration

CT Coronal View
Positive Beta-Catenin Stain

Stain
Negative S-100 Stain

Stain"