Nubbin sign | Radiology Signs

Answer:

The Nubbin Sign represents obstruction at the gallbladder neck. On hepatobiliary iminodiacetic acid (HIDA) scan imaging, the radionuclide fails to enter the gallbladder lumen, with only a small amount of tracer visible in the cystic duct region. This indicates impaired bile flow into the gallbladder, typically due to mechanical obstruction at the gallbladder neck or proximal cystic duct. Common causes include gallstones impacted at the neck, cystic duct stricture, or inflammation preventing normal biliary filling. The underlying pathological process involves cystic duct obstruction that prevents the normal accumulation of radiolabeled bile in the gallbladder.

Why is it called so?

The term “nubbin” describes something small and stunted, analogous to a pencil worn down to its last usable length. In this context, the sign represents the small, residual amount of tracer visible only in the diminished cystic duct region, rather than the expected robust filling of the entire gallbladder. The appearance resembles a small stub or nubbin of activity rather than the normal gallbladder reservoir appearance.

Pathophysiology

When the cystic duct becomes obstructed, the normal hepatic bile production cannot adequately fill the gallbladder. The radiolabeled tracer injected intravenously is normally taken up by hepatocytes and excreted into the biliary system. With cystic duct obstruction, most tracer flows through the common bile duct into the intestine, while minimal activity accumulates in the narrow, obstructed cystic duct. This creates the characteristic appearance of a small “nubbin” of activity at the gallbladder neck rather than gallbladder filling.