Why Gallstone Pain Shoots to the Right Shoulder: The Phrenic Nerve Pathway

Why Gallstone Pain Shoots to the Right Shoulder: The Phrenic Nerve Pathway

Overview of Referred Pain

Referred pain is a hallmark of visceral pathology, and few examples are as classic as gallbladder inflammation producing pain in the right shoulder. Understanding this phenomenon requires clarity on the sensory pathways of the gallbladder, the diaphragm, and the central processing of visceral afferents. The anatomical foundation lies in the shared innervation between the gallbladder’s peritoneal covering and the diaphragmatic peritoneum supplied by the phrenic nerve.

Visceral Pain from the Gallbladder

The gallbladder itself receives visceral sensory innervation primarily from the celiac plexus and sympathetic fibers arising from T7–T9 spinal segments, via the abdominal autonomic plexuses. This visceral afferent pathway explains the dull epigastric pain often seen in early biliary colic. However, when inflammation extends beyond the gallbladder lumen to involve the surrounding parietal peritoneum—especially the inferior surface of the diaphragm—the character and location of pain change dramatically.

Diaphragmatic Peritoneum and the Phrenic Nerve

The diaphragmatic peritoneum, particularly on its central portion, is lined by parietal peritoneum and is innervated by the phrenic nerve, which originates from the C3–C5 spinal cord levels. Irritation of this peritoneal surface by an inflamed gallbladder in cholecystitis activates somatic sensory fibers of the phrenic nerve. These fibers project directly to the dorsal horn neurons of C3–C5, which also receive sensory input from the skin over the shoulder region supplied by the supraclavicular nerves.

Dermatomes and Pain Projection to the Shoulder

Because visceral and somatic afferents converge onto the same second-order neurons, the brain misinterprets the source of the input. Although the actual stimulus is diaphragmatic irritation, the cortex localizes the sensation to the somatic territory of the C4 dermatome—the superior aspect of the shoulder. This is a classic example of convergence–projection theory in referred pain and aligns with the principles outlined in dermatome-based clinical correlation.

The right-sided predominance is straightforward: the gallbladder lies inferior to the right hemidiaphragm, meaning inflammatory processes in the gallbladder wall or pericholecystic abscesses directly irritate the right diaphragmatic peritoneum. Left-sided referred shoulder pain can occur when the left hemidiaphragm is irritated—for example, in splenic rupture—but gallbladder pathology almost always produces right-sided symptoms.

Clinical Correlation

In advanced cholecystitis, Murphy’s sign further reflects this anatomy. When the inflamed gallbladder contacts the examiner’s fingers during inspiration, diaphragmatic descent is abruptly halted due to pain transmitted via the phrenic nerve. The sudden cessation of inspiration is therefore a functional indicator of diaphragmatic peritoneal irritation.

Clinically, the presence of right shoulder pain in a patient with upper abdominal symptoms should raise immediate suspicion for gallbladder inflammation extending to the peritoneal surface. This referred pain pattern helps differentiate uncomplicated biliary colic from evolving acute cholecystitis, where somatic pain pathways become involved.

Ultimately, gallstone-related shoulder pain is not mysterious. It reflects a predictable anatomical pathway: the inflamed gallbladder irritates the diaphragmatic peritoneum, the phrenic nerve carries the sensation to C3–C5, and the brain projects the pain to the C4 dermatome—felt at the right shoulder.