Castell's sign

Lore & Background

Donald O. Castell, a George Washington Medical School graduate and Navy-trained gastroenterologist, first described his sign in the 1967 paper 'The Spleen Percussion Sign,' published in Annals of Internal Medicine. While stationed at the Great Lakes naval base in northern Illinois, Castell studied 20 male patients—10 with a positive percussion sign and 10 controls with negative percussion signs. He quantitatively measured each patient's spleen using chromium-labeled erythrocytes and a radioisotope photoscan. Castell found that controls had a mean spleen size of 75 cm² (range 57–75 cm²), while those with a positive sign had a mean size of 93 cm² (range 77–120 cm²). He concluded the technique was useful for identifying 'slight to moderate degrees of splenic enlargement' and constituted a 'valuable diagnostic technique.'

Reader's Guide

Castell's sign is performed by percussing the lowest intercostal space (eighth or ninth) in the left anterior axillary line with the patient supine, first in full expiration and then in full inspiration. A change from resonant on expiration to dull on inspiration is considered positive, indicating that the inferior pole of an enlarged spleen has moved into that space. The 1993 systematic review by the Rational Clinical Examination found Castell's sign to be the most sensitive physical examination maneuver for detecting splenomegaly, with a sensitivity of 82% and specificity of 83%, outperforming palpation and other percussion signs. However, its utility depends on clinical context: to achieve a positive predictive value over 90%, the pretest probability must be 70%; a pretest probability of 30% or less yields a negative predictive value over 90%. Limitations include gross splenomegaly or profuse fluid in the stomach or colon causing absence of a resonant note on expiration, and reduced reliability in obese individuals and depending on post-prandial timing. Despite these limitations, Castell's sign remains a valuable part of the abdominal exam when combined with other clinical information.

Did You Know?

• Castell's sign is an alternative to percussion over Traube's space for detecting splenomegaly.
• The sign was first described by Donald O. Castell in a 1967 paper in Annals of Internal Medicine.
• Castell studied 20 male patients using chromium-labeled erythrocytes and radioisotope photoscan to measure spleen size.
• The 1993 Rational Clinical Examination systematic review found Castell's sign had 82% sensitivity and 83% specificity for splenomegaly.

Clinical Significance & Diagnostic Utility

Castell's sign occupies a distinctive niche in abdominal physical examination as a percussion-based maneuver designed to detect splenomegaly. Unlike palpation, which requires the spleen to be so massively enlarged that it drops well below the costal margin, Castell's method can identify even slight to moderate degrees of enlargement. This makes it particularly valuable in a clinical landscape where splenomegaly—whether from infectious mononucleosis, thalassemia, or cirrhotic liver disease—remains one of the more elusive findings to confirm at the bedside. The sign is not meant to stand alone; rather, it functions as a component within a broader diagnostic rubric. When combined with other clinical information, its positive predictive value rises substantially, helping clinicians decide whether to pursue further imaging. In advanced physical diagnosis courses, it is considered a superior teaching tool compared to other spleen percussion signs and to palpation, given its higher sensitivity.

Technique & Physiological Rationale

The maneuver requires the patient to lie supine while the examiner percusses the eighth or ninth intercostal space along the left anterior axillary line. The critical element is the respiratory cycle: the examiner first notes the percussion quality at full expiration, then repeats at full inspiration. A positive sign is indicated when the note shifts from resonant on expiration to dull on inspiration. The physiological logic is elegant. During expiration, air-filled structures such as the stomach or the splenic flexure of the colon occupy that region, producing a resonant tone. Upon inspiration, the diaphragm descends and pulls the spleen inferiorly along the posterolateral abdominal wall. If the organ is enlarged enough for its inferior pole to reach the eighth or ninth intercostal space, solid splenic tissue replaces the air-filled structures, yielding a dull percussion note. Castell himself noted limitations: gross splenomegaly or large volumes of gastric or colonic fluid can eliminate the resonant baseline, and subsequent literature has flagged reduced reliability in obese patients and those examined shortly after eating.

Evidence & Interpretation

The 1993 Rational Clinical Examination systematic review positioned Castell's sign as the most sensitive bedside maneuver for detecting splenomegaly, outperforming both Nixon's sign and direct palpation, with a sensitivity of 82 percent and a specificity of 83 percent. However, the numbers carry important caveats. In asymptomatic patients with very low clinical suspicion, physical examination alone is insufficient to confirm splenomegaly because the pretest probability is too low. Grover and colleagues recommended a preexamination clinical suspicion exceeding 10 percent to make the sign diagnostically useful, yet even at that threshold the positive predictive value reaches only about 35 percent. To push the positive predictive value above 90 percent, the pretest probability must climb to roughly 70 percent. Conversely, ruling out an enlarged spleen is more straightforward: a pretest probability of 30 percent or less yields a negative predictive value exceeding 90 percent. These figures underscore that Castell's sign is most powerful when embedded within a clinical context that already raises reasonable suspicion.

Origins & Historical Context

Donald O. Castell, a gastroenterologist trained in the Navy and a graduate of George Washington Medical School, first described the maneuver in a 1967 paper titled 'The Spleen Percussion Sign' in the Annals of Internal Medicine. While stationed at the Great Lakes naval base in northern Illinois, he conducted a focused study of 20 male patients—10 with a positive percussion sign and 10 controls with a negative one. Each patient's spleen was then quantitatively measured using chromium-labeled erythrocytes combined with a radioisotope photoscan. The results were striking: the control group had a mean spleen area of 75 square centimeters (range 57 to 75), while the positive-sign group averaged 93 square centimeters (range 77 to 120). Castell concluded that his percussion technique could identify slight to moderate degrees of splenic enlargement and constituted a valuable diagnostic tool. The sign has since been debated in medical literature alongside other splenomegaly signs, yet it retains its position as the most sensitive bedside option.

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