Perianal mucinous adenocarcinoma arising from perianal fistula
Presentation
History of chronic right perianal fistula now complains of perianal pain.
Patient Data
Right anal and perianal exophytic lobulated soft tissue mass lesion. It elicits low signal on T1 and very bright T2/STIR signal with diffusion restriction and vivid post contrast enhancement. The mass is seen within the right anterior aspect of the anal canal, with an exophytic component within the right ischiorectal fossa. An adjacent short fistula tract is noted.
Bilateral enlarged inguinal lymph nodes, larger on the right, likley metastatic.
Left ischiorectal old fibrotic fistulous tract.
Case Discussion
This is a pathologically proven perianal mucinous adenocarcinoma arising from chronic perianal fistula.
The case shows the typical location (perianal) and the signal intensity (bright on T2 and STIR) of the perianal mucinous adenocarcinoma with associated adjacent perianal fistula.
Fistula-associated perianal mucinous adenocarcinoma is a very rare malignant transformation of chronic fistula-in-ano. The exact incidence of perianal mucinous adenocarcinoma is unknown. Some documented risk factors include perianal fistulous disease, inflammatory bowel disease and diabetes 1. This condition's pathophysiology is partly believed to be secondary to chronic inflammatory changes.
Most perianal mucinous adenocarcinoma patients present with anal pain or rectal bleeding.
The absence of a tumor within the lumen of the bowel and the slow growth of a lesion hidden within the ischioanal fossa or perineum make early diagnosis difficult.
Several characteristic findings on MRI provide important diagnostic information on patients with this condition.MRI accurately shows the perianal anatomy and the detailed extensions and staging of the perianal tumors. Mucinous colorectal carcinomas contain large pools of extracellular mucin lined by columns of malignant cells, cords and vessels, which give rise to a typical mesh-like internal structure. The mucin, which forms the major tissue component of mucinous tumors, has high signal intensity on T2-weighted fast SE images. A fistula between the mass and the anus is a characteristic finding of mucinous adenocarcinoma arising from fistula-in-ano on MRI 2.
Differential diagnoses include perianal abscess and fistula.
Unable to process the form. Check for errors and try again.