Spontaneous dissection of the SMA is a rare occurrence, especially when not associated with aortic dissection. 1 Only sporadic case reports of the sonographic demonstration of isolated spontaneous dissection of the SMA have been published, 2,3 and for the most part color Doppler imaging is not included. We report the sonographic findings in an asymptomatic patient with isolated dissection of an SMA aneurysm and discuss the unique flow dynamics seen by color Doppler sonography. CASE REPORTA 58 year old man, with no past significant medical history, was referred for renal sonography as part of an evaluation for flank and low back pain. He had no abdominal pain, no postprandial discomfort or nausea, and no history of abdominal trauma. His physical examination, vital signs, electrocardiograms, and radiographs of the abdomen were all normal. Laboratory test results were all within normal limits.Abdominal sonography showed normal kidneys. A small anechoic structure, however, was noted anterior to the aorta in the upper abdomen. Transverse and longitudinal views revealed that the structure was an aneurysm of the SMA, localized to an area 4 cm from the origin of the artery from the aorta. A fine linear echogenic structure, representing an intimal flap, was seen separating the aneurysm into anterior and posterior compartments (Fig. 1). The vascular nature and connection to the SMA was confirmed by color Doppler sonography. Flow in the anterior (true lumen) compartment was antegrade, whereas flow in the posterior (false lumen) compartment was continuously reversed. This produced a checkered pattern in the aneurysm, with alternating red and blue areas on both sides of the flap, representing flow in opposite directions relative to the transducer position (Fig. 2). CT with contrast enhancement revealed a thin hypodense line within the SMA, separating two distinct enhancing lumina (Fig. 3). Dissection localized to the proximal part of the SMA was found at angiography (Fig. 4). Since the patient was asymptomatic, the case was managed conservatively. Follow-up sonography showed no change over 16 months.