What causes the rat tail sign on barium swallow?
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Answer:
The rat tail sign is smooth, symmetrical, gradually tapering narrowing of the distal oesophagus to a fine point at the oesophagogastric junction, with proximal dilatation and retained food and fluid above it. It is the barium appearance of achalasia and is synonymous with the bird beak sign. The critical distinction is from pseudoachalasia, secondary achalasia caused by tumour at or near the junction, which can reproduce the tapered segment exactly. Features favouring malignancy are a narrowed segment longer than about 3.5 cm, an oesophagus dilated to 4 cm or less despite a marked stricture, eccentric rather than concentric narrowing, mucosal irregularity, nodularity or shouldering, and a short clinical history with weight loss in an older patient. Any of these warrants endoscopy and cross-sectional imaging. The timed barium oesophagram, which measures the residual barium column height at one, two and five minutes, quantifies emptying and is the standard tool for assessing response to pneumatic dilatation, myotomy or POEM.
Why is it called so?
The distal oesophagus tapers smoothly to a thin point like the tail of a rat.
Pathophysiology
Achalasia results from progressive loss of inhibitory ganglion cells in the myenteric plexus of the distal oesophagus, so the lower oesophageal sphincter fails to relax with swallowing and peristalsis is lost in the smooth-muscle segment. The persistently contracted sphincter produces a short, smooth, concentric narrowing, while the column of retained material above it dilates the body of the oesophagus over years. Because the narrowing is functional and the mucosa is intact, the tapered segment stays smooth and symmetrical; a tumour infiltrating the same region distorts the mucosa and produces the asymmetry and irregularity that betray pseudoachalasia.
Alternative names: Bird beak sign, beak sign of achalasia (distinct from the beak sign of aortic dissection)
Other associated named signs: Corkscrew oesophagus and rosary bead oesophagus of spastic disorders, and the feline oesophagus
References
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
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