Figure 5c. Bilateral psoas neurofibromas in a 32-year-old woman with NF1 who presented to the emergency department with right lower abdominal pain and nausea. (a) Longitudinal sonogram of the right lower quadrant shows a 10-cm oval heterogeneously hypoechoic mass. (b, c) Intravenous contrast material–enhanced CT scans show a hypoattenuating mass (arrow in b) containing focal areas of high attenuation arising from the right psoas muscle and a smaller hypoattenuating mass (arrowhead in c) in the left psoas muscle. (d) Photograph of the cut surface of the resected specimen from the right psoas muscle shows an oval, rubbery, tan mass surrounded by a thin fibrous capsule.