Double donut sign
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The double donut sign is a radiological/sonographic finding with two distinct clinical contexts — both involving a "ring within a ring" appearance. Here is a comprehensive breakdown:
Double Donut Sign
1. Intussusception (Most Classic Association)
The double donut sign is most commonly associated with intestinal intussusception, particularly on transverse-plane ultrasound.
Appearance:
- On cross-section, the intussuscepted bowel produces two concentric hyperechoic rings separated by a hypoechoic layer, creating a "donut within a donut" or "target" appearance
- The outer ring = the intussuscipiens (receiving bowel wall)
- The inner ring = the intussusceptum (invaginated bowel segment)
- The hypoechoic halo between them represents edematous mesentery and bowel wall
Clinical significance:
- Seen in ileocolic intussusception, the most common type in children (peak age: 3 months – 6 years)
- Ultrasound sensitivity for intussusception is >97% when this sign is present
- Presence of a lead point (e.g., Meckel's diverticulum, lymphoma, polyp) should be suspected in older children and adults
- Management: air or hydrostatic enema reduction; surgery if peritonitis or failed reduction
2. Hypertrophic Pyloric Stenosis (HPS)
The related "donut sign" (single) on ultrasound is the hallmark of HPS — a hypoechoic muscular ring surrounding a central echogenic mucosa on transverse view. The double donut sign in this context refers to bilateral views of the pylorus showing symmetric thickening.
Diagnostic criteria:
| Parameter | Threshold |
|---|---|
| Pyloric muscle thickness | ≥ 3–4 mm |
| Pyloric channel length | ≥ 14–17 mm |
| Pyloric diameter | ≥ 10–14 mm |
3. Ovarian Torsion / Pelvic Pathology
The double donut sign has also been described in ovarian torsion on ultrasound, where concentric rings represent the twisted ovarian tissue layers, though this usage is less standardized.
Comparison of Key Contexts
| Feature | Intussusception | HPS |
|---|---|---|
| Age group | 3 months – 6 years (peak) | Neonates (3–6 weeks) |
| Modality | Ultrasound (transverse) | Ultrasound (transverse) |
| Sign appearance | Two concentric rings | Single ring (mucosa + muscle) |
| Clinical presentation | Colicky pain, "currant jelly" stools, palpable mass | Projectile non-bilious vomiting, olive mass |
| Management | Enema reduction / surgery | Pyloromyotomy (Ramstedt) |
Imaging
Transverse abdominal ultrasound showing the donut sign in hypertrophic pyloric stenosis. The peripheral hypoechoic ring represents the thickened muscularis; the central echogenic core is the compressed mucosa. Electronic calipers measure muscle thickness.
Key takeaway: The double donut sign on transverse ultrasound is most clinically important as a marker of intussusception, where it reflects the telescoping of one bowel segment into another. Recognition prompts urgent management to prevent bowel ischemia and perforation.
Double donut sign in dengue
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Double Donut Sign in Dengue
The double donut sign (also called the double-wall sign or halo sign) in dengue refers to a gallbladder ultrasound finding caused by marked edema of the gallbladder wall — a direct consequence of plasma leakage from increased vascular permeability.
Pathophysiology
During the critical phase of dengue (typically days 4–6, coinciding with defervescence), a surge in vascular permeability causes plasma to leak out of the intravascular compartment into tissues and third spaces. The gallbladder wall, being highly vascularized and loosely supported, accumulates edema fluid between its layers, producing the characteristic layered appearance on ultrasound.
Ultrasound Appearance
On B-mode ultrasound, the edematous gallbladder wall shows:
- A layered / striated appearance — alternating echogenic and hypoechoic bands within the wall
- The double donut / double-wall configuration is best seen on transverse cross-section: a hypoechoic (dark) halo surrounds the echogenic inner wall layer, creating two concentric rings
- Gallbladder wall thickness (GBWT) ≥ 3–4 mm is considered abnormal (normal: ~2–3 mm); in severe dengue, GBWT can exceed 6 mm
| Parameter | Normal | Dengue (Critical Phase) |
|---|---|---|
| GBWT | ≤ 0.3 cm | ≥ 0.4–0.6 cm or more |
| Wall appearance | Thin, echogenic | Layered, hypoechoic halo |
| Associated fluid | None | Pericholecystic fluid, ascites, pleural effusion |
Clinical Significance
| Aspect | Detail |
|---|---|
| Timing | Critical phase: days 4–6 of illness |
| Indicator of | Significant plasma leakage / dengue with warning signs |
| Severity marker | GBWT correlates with degree of vascular permeability |
| Associated findings | Ascites, bilateral pleural effusions, periorbital edema |
| Risk | Flags patients at risk for dengue shock syndrome (DSS) and hemorrhagic complications |
Gallbladder wall thickening ≥ 3 mm on ultrasound is recognized as a warning sign that prompts close monitoring and consideration of IV fluid therapy.
Imaging
Transverse abdominal ultrasound: (A) Normal gallbladder wall measuring 0.24 cm. (B) Pathologically thickened gallbladder wall measuring 0.62 cm in a patient with severe dengue, showing a layered hypoechoic double-wall/double donut appearance — indicative of plasma leakage.
Differential Diagnosis of Gallbladder Wall Thickening
Dengue is not the only cause — the finding must be interpreted in clinical context:
| Cause | Distinguishing Feature |
|---|---|
| Dengue fever | Fever + thrombocytopenia + dengue serology |
| Acute cholecystitis | Tenderness, Murphy's sign, gallstones |
| Hypoalbuminemia (cirrhosis, nephrotic syndrome) | Low albumin, chronic disease |
| Congestive heart failure | Elevated JVP, cardiomegaly |
| Hepatitis | Elevated transaminases, jaundice |
| Ascites (any cause) | Requires correlation |
Bottom line: The double donut sign in dengue is a sonographic marker of gallbladder wall edema secondary to plasma leakage. Its presence during the febrile illness should prompt classification of the patient as having dengue with warning signs (per WHO 2009 criteria), warranting inpatient monitoring, serial hematocrit measurements, and judicious fluid management. (Clinical Management of Arboviral Diseases: Dengue, p. 64)
Double donut sign in ct scan mri scan in dengue
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The retrieved database does not have specific CT/MRI literature on this topic, so the answer below draws on established radiology knowledge.
Double Donut Sign in Dengue on CT and MRI
The double donut sign is primarily described on ultrasound in dengue, but its morphological basis — layered gallbladder wall edema from plasma leakage — is equally visible on CT and MRI, where the sign appears with even greater anatomical clarity.
On CT Scan
Appearance
On contrast-enhanced CT (CECT) abdomen, the edematous gallbladder wall produces a double-layer / double donut configuration in cross-section:
| Layer | CT Appearance |
|---|---|
| Inner layer (mucosa + submucosa) | Hyperattenuating (enhances with contrast) |
| Middle layer (submucosal edema) | Hypoattenuating (low-density fluid/edema) |
| Outer layer (serosa/muscularis) | Iso- to slightly hyperattenuating |
This alternating density produces the "double donut" or "halo" sign on axial sections — two concentric rings of differing attenuation around the gallbladder lumen.
Additional CT Findings in Dengue
| Finding | CT Appearance |
|---|---|
| Gallbladder wall thickening | Wall > 3 mm, stratified/layered |
| Pericholecystic fluid | Low-density fluid around GB fossa |
| Ascites | Free fluid in peritoneal cavity |
| Pleural effusions | Bilateral > unilateral; right-sided predominance |
| Hepatosplenomegaly | Enlarged liver and/or spleen |
| Peripancreatic edema | Stranding around pancreas (in severe cases) |
| Retroperitoneal edema | Fat stranding |
CT is not the first-line modality for dengue (ultrasound is preferred due to cost, availability, and lack of radiation), but CT is used when complications like hemorrhage, bowel involvement, or abdominal organ pathology need to be excluded.
On MRI
Appearance
MRI provides the most detailed characterization of the layered gallbladder wall edema:
| Sequence | Appearance |
|---|---|
| T1-weighted | Inner wall isointense; edematous middle layer hypointense |
| T2-weighted | Middle edematous layer markedly hyperintense (bright) — best sequence for the double donut sign |
| T1 post-gadolinium | Enhancement of inner mucosal and outer serosal layers with non-enhancing edematous middle layer — classic "sandwich" / double donut pattern |
| MRCP | Can assess biliary involvement; GB wall thickening clearly delineated |
On T2 axial images, the cross-sectional view of the gallbladder shows:
- Bright (hyperintense) edematous halo = inner ring
- Hypointense lumen content
- Bright pericholecystic fluid surrounding the outer wall ...producing the double donut appearance.
MRI in Dengue Encephalitis / Neurological Dengue
MRI of the brain and spinal cord is used when dengue affects the CNS (dengue encephalitis/encephalopathy):
| Location | MRI Finding |
|---|---|
| Bilateral thalami | T2/FLAIR hyperintensities (most characteristic) |
| Cerebral cortex | Diffuse edema, FLAIR signal changes |
| Cerebellum | Cerebellar edema, T2 signal changes |
| Basal ganglia | Hyperintensities on T2/FLAIR |
| Spinal cord | Myelitis pattern (rare) |
| White matter | Leukoencephalopathy (rare) |
These brain MRI findings do not produce a "double donut" sign per se — that sign is specific to the gallbladder wall in the abdominal context.
Summary Comparison Across Modalities
| Feature | Ultrasound | CT | MRI |
|---|---|---|---|
| Double donut sign | Hypoechoic halo around echogenic wall | Hypoattenuating edema band between enhancing layers | T2 hyperintense edema band between enhancing layers |
| Best sequence/mode | B-mode transverse | CECT axial | T2 axial / post-Gad T1 |
| Added value | Bedside, no radiation, first-line | Detects hemorrhage, complications | Best soft tissue resolution, brain involvement |
| Limitation | Operator-dependent | Radiation, contrast risk | Cost, availability, time |
| Role in dengue | Screening and monitoring | Second-line / complications | CNS dengue, complex cases |
Key point: Regardless of modality, the double donut sign in dengue reflects submucosal gallbladder wall edema secondary to plasma leakage — a marker of the critical phase. On CT and MRI, the stratified wall enhancement pattern makes this even more conspicuous than on ultrasound, but ultrasound remains the gold standard for monitoring dengue-related plasma leakage due to practicality. (Clinical Management of Arboviral Diseases: Dengue, p. 64)
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Double Donut Sign in Brain CT/MRI — with Dengue Context
The double donut sign in brain imaging is a distinct entity from the abdominal gallbladder sign. In the CNS, it refers to bilateral symmetrical thalamic lesions on MRI that, when viewed on axial sections, produce two oval/round hyperintense signals flanking the third ventricle — resembling two donuts side by side.
What Is the Double Donut Sign on Brain MRI?
On axial T2/FLAIR MRI, bilateral thalamic hyperintensities appear as:
- Two symmetrical, ovoid, hyperintense lesions in the bilateral thalami
- Flanking the third ventricle centrally
- Creating a "double donut" or "owl eye" configuration
- With possible mass effect on the third ventricle and posterior limbs of the internal capsule
This sign is a hallmark of bilateral thalamic involvement by viral encephalitis, and dengue encephalitis is one of the most important causes.
Double Donut Sign in Dengue Encephalitis
Pathophysiology
Dengue causes CNS involvement through:
- Direct neurotropism — DENV crosses the blood-brain barrier and infects neurons/glial cells
- Immune-mediated injury — cytokine storm, autoimmune demyelination
- Metabolic encephalopathy — hepatic failure, electrolyte disturbance, SIADH
- Microvascular injury — thrombocytopenia-related microhemorrhages, cerebral edema
The thalami are particularly vulnerable due to their rich vascularity and high metabolic demand.
MRI Sequences and Findings
| Sequence | Finding in Dengue Encephalitis |
|---|---|
| T2-weighted (axial) | Bilateral thalamic hyperintensities — the double donut sign; well-defined oval lesions |
| FLAIR | Confirms edema and inflammation in thalami; suppresses CSF to better delineate lesions |
| DWI | Restricted diffusion if cytotoxic edema (acute ischemic/necrotic component) |
| SWI / GRE | Hypointense foci with blooming = microhemorrhages within thalamic lesions |
| T1 post-Gadolinium | Variable; may show ring or patchy enhancement in severe cases |
Imaging
Axial T2 MRI: Large bilateral symmetrical hyperintense oval lesions in both thalami (right > left, black arrow), with mild mass effect on the third ventricle and posterior limbs of the internal capsules. This is the classic double donut sign of dengue encephalitis.
(a) Axial T2: Symmetric bilateral thalamic hyperintensities (arrows). (b) Coronal FLAIR: Hyperintense edema lateral to the third ventricle in both thalami. (c) Axial SWI: Multiple hypointense foci with blooming artifact = thalamic microhemorrhages — indicating hemorrhagic dengue encephalitis.
CT Findings in Dengue Encephalitis
CT is less sensitive than MRI but may show:
| Finding | Appearance on CT |
|---|---|
| Bilateral thalamic hypodensity | Symmetric low-density areas in both thalami (the CT correlate of the double donut sign) |
| Cerebral edema | Sulcal effacement, loss of grey-white differentiation |
| Hemorrhagic transformation | Hyperdense foci within thalami or elsewhere |
| Herniation | In severe cases with massive edema |
| Normal CT | CT can be entirely normal early — MRI is far superior |
CT may miss subtle thalamic lesions that are clearly visible on T2/FLAIR MRI. A normal CT does not exclude dengue encephalitis.
Differential Diagnosis of the Double Donut Sign (Bilateral Thalamic Lesions)
| Condition | Distinguishing Features |
|---|---|
| Dengue encephalitis | Dengue serology +ve, fever, thrombocytopenia, endemic area |
| Japanese Encephalitis (JEV) | Most common cause; similar MRI pattern; JEV IgM in CSF |
| West Nile Virus encephalitis | Involves thalamus, basal ganglia, brainstem; WNV serology |
| Wernicke's encephalopathy | Thiamine deficiency; also involves mammillary bodies and periaqueductal grey |
| Deep cerebral venous thrombosis | Bilateral thalamic venous infarcts; MRV shows thrombosed deep veins |
| Artery of Percheron infarct | Single arterial territory supplying both thalami; DWI positive |
| Creutzfeldt-Jakob disease (CJD) | "Pulvinar sign"; rapidly progressive dementia; DWI striking |
| Acute necrotizing encephalopathy | Children; bilateral thalamic necrosis; often post-viral/influenza |
| Osmotic demyelination | Central pontine + extrapontine myelinolysis; associated with rapid Na correction |
| CNS lymphoma / toxoplasmosis | HIV context; ring-enhancing lesions (Harrison's, p. 5928) |
Summary
| Feature | Detail |
|---|---|
| Sign | Double donut sign = bilateral symmetrical thalamic hyperintensities on axial T2/FLAIR |
| Best modality | MRI (T2, FLAIR, DWI, SWI) |
| CT value | Low-density thalamic changes; less sensitive; hemorrhage detection |
| Dengue mechanism | Direct neurotropism + immune injury + microvascular hemorrhage |
| Key additional finding | SWI microhemorrhages suggest hemorrhagic dengue encephalitis |
| Clinical correlation | Altered consciousness, seizures, fever, thrombocytopenia in dengue-endemic region |
The double donut sign on brain MRI in the right clinical context (fever + thrombocytopenia + dengue-endemic region) should prompt dengue IgM/IgG serology, CSF dengue PCR, and Japanese Encephalitis serology to differentiate, as management implications differ. (Harrison's Principles of Internal Medicine, 21st ed., p. 4126; p. 5928)
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