Radiology signs
A dictionary of classic named signs across every modality and body system. Each entry explains what the sign looks like on imaging and what it means, with the underlying mechanism, associated conditions and high-yield teaching pearls.
Signet ring sign
Bronchial dilatation with a broncho-arterial ratio greater than 1, the defining feature of bronchiectasis.
Comet tail sign
Rounded atelectasis, a benign folded region of collapsed lung tethered to adjacent pleural disease.
Air crescent sign
Typically an aspergilloma (fungus ball) within a pre-existing cavity, or the recovery phase of angioinvasive aspergillosis.
Halo sign
Perilesional haemorrhage, classically around an angioinvasive fungal infection in the immunocompromised host.
Tree-in-bud sign
Small-airway (bronchiolar) disease with impaction, most often infectious bronchiolitis.
Golden S sign
Lobar collapse caused by a central obstructing mass, raising concern for bronchogenic carcinoma.
Silhouette sign
The opacity abuts a specific structure, allowing anatomical localisation of the disease.
Deep sulcus sign
A pneumothorax in the supine patient, where free pleural air collects anteriorly and basally.
Continuous diaphragm sign
Pneumomediastinum, with air tracking between the heart and diaphragm.
Rigler sign
Pneumoperitoneum, with free intraperitoneal gas outlining the outer bowel wall.
Football sign
Massive pneumoperitoneum, classically in a neonate with a perforated viscus.
Target (doughnut) sign
Intussusception, where one bowel segment telescopes into the adjacent segment.
Coffee bean sign
Sigmoid volvulus, a closed-loop obstruction from twisting of the sigmoid colon.
Bird beak sign
A smoothly tapered obstruction, seen at the gastro-oesophageal junction in achalasia and at the twist point in volvulus.
String of pearls sign
Small bowel obstruction with fluid-filled loops.
Double bubble sign
Proximal duodenal obstruction, classically duodenal atresia in the neonate.
Whirl sign
Midgut volvulus, usually in the setting of intestinal malrotation.
Comb sign
Active mesenteric hyperaemia adjacent to actively inflamed bowel.
Empty delta sign
Dural venous sinus thrombosis, most often of the superior sagittal sinus.
Dawson fingers
Demyelinating plaques characteristic of multiple sclerosis.
Molar tooth sign
The imaging hallmark of Joubert syndrome and related ciliopathies.
Hot cross bun sign
Selective degeneration of pontine transverse fibres, classically in multiple system atrophy.
Ivy sign
Slow leptomeningeal collateral flow, characteristic of moyamoya disease.
Codman triangle
Aggressive periosteal reaction, indicating a fast-growing bone lesion.
Sunburst (sunray) sign
An aggressive periosteal reaction typical of osteosarcoma.
Fallen fragment sign
A fluid-filled simple (unicameral) bone cyst that has sustained a pathological fracture.
Sail sign
At the elbow it indicates a joint effusion (often occult fracture); in the neonatal mediastinum it is the normal thymus.
Steeple sign
Subglottic oedema, classically due to croup (laryngotracheobronchitis).
Thumb sign
Epiglottitis, a potentially life-threatening supraglottic infection.
Westermark sign
Regional decreased perfusion suggestive of acute pulmonary embolism.