Imaging diagnosis of anorectal malignant melanoma

Abstract

Objective To discuss the diagnostic value of CT and MRI for primary anorectal malignant melanoma(AMM).Methods Seven patients(3 males and 4 females) with AMM confirmed pathologically were analyzed retrospectively,which were examined by CT(n =6) and 1.5T MRI(n = 1).Results AMM presented as bulky intraluminal fungating masses without causing obstruction(n =5) and irragular rectal wall thickening(n =2).Three cases had perirectal infiltration with 1 case extended to the presacral space,Five cases had perirectal enlarged lymph nodes with 1 case larger than 3 cm in diameter.Nonenhanced CT showed a hypodense lesion and Enhanced CT manifested slight enhancement(n = 2) and mild enhancement(n = 4).The tumor scanned by MRI depicted high intensity on T1WI and low intensity on T2WI,so did the enlarged lymph nodes and bone metastasis.Fat-saturation T1WI significantly improved the extention of tumor and detection of metastasis.Conclusion Bulky intraluminal fungating masses without causing obstruction,perirectal infiltration and enlarged lymph nodes may be helpful to diagnose AMM.MRI is especially useful for differentiating melanotic AMM from other rectal tumors. Key words: Anus; Rectum; Melanoma; Tomography; X-ray computed; Magnetic Resonance Imaging