Stepwise progression of familial adenomatous polyposis-associated desmoid precursor lesions demonstrated by a novel CT scoring system.

INTRODUCTION

Desmoids are rare, locally aggressive but nonmetastasizing clonal proliferations of fibroblasts that occur both sporadically and in association with familial adenomatous polyposis. Most occur in intra-abdominal sites, where they may lead to major morbidity and mortality. A proposed desmoid precursor lesion occurs in the mesentery of one-third of patients with familial adenomatous polyposis, and postoperative mesenteric fibromatosis has been identified in 20 percent of such patients. True desmoids occur in 10 percent, which suggests a model of development in which the phenotype becomes increasingly severe in a manner analogous to the adenoma-carcinoma sequence. This work aimed to confirm such a progression.

METHODS

A five-point CT scoring system for mesenteric fibromatosis and desmoids was devised and validated, and in doing so, their incidence was observed. In the second part of the study, seven patients known to have a precursor lesion underwent abdominal CT a median of 27.5 months after the surgery that identified the lesion. Scans were assessed by the scoring system and compared with those of a matched control group of familial adenomatous polyposis patients.

RESULTS

The CT scoring system was reliable and reproducible. Of 103 scans of asymptomatic patients with familial adenomatous polyposis, mesenteric fibromatosis and desmoid tumors were identified in 21 and 2 percent, respectively. In the follow-up of patients with desmoid precursor lesions, those in the precursor lesion group had a significantly greater degree of mesenteric fibromatosis and desmoid formation than their corresponding controls (P = 0.009, Mann-Whitney U test).

CONCLUSION

A reliable CT scoring system for mesenteric fibromatosis and desmoid tumors in familial adenomatous polyposis is presented. Results with this system provide further evidence for a stepwise progression in the development of desmoids.