Frostberg’s inverted three sign

Excerpt

Nils Frostberg originally described the sign that bears his name in three patients that showed a peculiar deformity in the duodenum in what were then called roentgenograms back in 1938 [1]. This radiological sign is classically associated with pancreatic and duodenal carcinomas, but it has also been described in benign conditions (e.g., chronic pancreatitis, duodenal ulcers) [2, 3], and even one of the patients in Frostberg’s initial description was found to have microscopic findings of pancreatitis on necropsy. It corresponds to an increased amplitude and deformation of the duodenal curve secondary to traction of the second portion of the duodenum and/or an increase in size of its surrounding structures (ampulla of Vater, Santorini’s duct, or the head of the pancreas). These abnormalities change the typical “C” morphology of the duodenal curve to an “inverted three” morphology, as shown in Fig. 1. A contrast-enhanced CT correlation (Fig. 2) shows a hyperdense lesion located in the head of the pancreas (arrow), and a hypodense lesion in the liver adjacent to the gallbladder (arrowhead). This patient was diagnosed with a metastatic well-differentiated neuroendocrine tumor.

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