Pulmonary Infarction

Chest x-ray demonstrates a peripheral airspace opacity (arrows) that has a wedge-shaped configuration and a blunt medial apex pointing toward the hilum

Coronal-reformatted CT images confirm the presence of airspace opacity in the right middle lobe (arrows) with an embolus in the corresponding segmental pulmonary artery (arrowhead)

Facts: 

• Pulmonary embolic obstruction can occur with or without resultant pulmonary infarction
• In pulmonary embolism with infarction, process begins as "incomplete" infarct (intra-alveolar hemorrhage without necrosis of alveolar wall), which can go on to necrosis "infarct" especially in patients with underlying unhealthy lung
• On CXR, infarct is seen as a wedge-shaped, pleural-based consolidation with a rounded convex apex directing toward the hilum "Hampton hump"
• Often occurs in lower lobes
• Heals with scar formation

Reference

Dalen JE. Pulmonary embolism: what have we learned since Virchow? Chest 2002; 122:1440-1456.

Color Doppler Twinkling Artifact

Longitudinal images of the left kidney show a stone (arrow) in the lower pole with posterior acoustic shadowing and the color Doppler twinkling artifact (short arrows).

Facts:

• Rapidly alternating red and blue signal behind a highly reflective structure on color Doppler US
• Useful diagnostic signs especially for urinary calculi detection and improved diagnostic confidence
• Can also be seen in calcifications in various tissues, biliary stones, encrusted indwelling urinary stents, gallbladder adenomyomatosis and bile duct hamartomas
• Two proposed mechanisms:
• Phase jitter - intrinsic machine noise causing random fluctuation of acoustic waves
• Acoustic waves hitting a rough interface producing complex beam pattern with multiple reflections

Reference

Kim HC, et al. Color Doppler twinkling artifacts in various conditions during abdominal and pelvic sonography. J Ultrasound Med 2010; 29:621.

Mosaic Pattern of Lung Attenuation

Axial CT images of the chest in lung windows (inspiratory images) shows multilobular areas of variable lung attenuation (mosaic pattern) with dark areas showing diminished size/numbers of pulmonary vessels indicating that these dark areas are abnormal. 

Facts:

• Lobular or multilobular distribution of variable lung attenuation
• Three possible groups of etiologies: small-airway, vascular and infiltrative disease 
• Additional findings are helpful to distinguish the three causes

Making Decisions

1. Dark or white areas are abnormal? Looking at size and number of vessels in both regions. If they are similar, the "white" is abnormal (meaning it is ground glass abnormality). If the size/number of vessels in dark areas are decreased, this is either small-airway or vascular pathology
2. If the "white" is abnormal, look for differentials of ground glass opacity (GGO)
3. If the "dark" is abnormal, look at expiratory phase scanning. If air trapping is present, this is small-airway disease. If there is no air trapping, this is likely vascular cause
4. If expiratory scanning was not available, look at clinical features.  Dyspnea, cough, wheezing and response to bronchodilators are common in patients with small-airway disease and infrequent in vascular lung disease

Our case: We did not perform expiratory scan in this patient but given clinical scenario, the dark areas likely represent mosaic pattern from known chronic pulmonary embolism with pulmonary hypertension. 

Reference:

Stern EJ, et al. CT mosaic pattern of lung attenuation: distinguishing different causes. AJR 1995;165:813.

Focal Hepatic Hot Spot Sign

An axial CT image shows a geographic area of hypervascularity (arrow) in segment IV of the liver. Note enlarged subcutaneous collateral vessels (arrowheads)

Facts: Focal Hepatic Hot Spot

• Focal area of enhancement in segment IV of liver due to presence of SVC obstruction
• Occurs due to portosystemic shunting between SVC and portal vein
• With SVC obstruction, blood may flow through internal mammary vein --> paraumbilical vein --> portal vein 
• Other causes of focal hot spots: Budd-Chiari syndrome (caudate lobe), liver abscess, hemangioma, FNH and HCC

Three Routes of Bypass of Venous Blood in Central Thoracic Venous Obstruction

1. Superior route: from subclavian vein to anterior jugular venous system (occuring in subclavian or brachiocephalic venous obstruction)
2. Posterior route: azygos-hemiazygos and paravertebral systems
3. Anterolateral route: like in our case, this is via anterior intercostal, internal mammary and long thoracic veins to IVC

Reference:

Maldjian PD, Obolevich AT, Cho KC. Focal enhancement of the liver on CT: a sign of SVC obstruction. J Comput Assist Tomogr 1995;19:316-8

The Fat Pad Sign

A lateral radiograph of the elbow shows a posterior fat pad sign (arrows) and elevation of the anterior fat pad (arrowheads) in a patient with a radial neck fracture (seen anteriorly on this image).

Facts

• Normal: elbow fat pads are intracapsular but extrasynovial, they are visible anteriorly to the elbow joint but not posteriorly.
• Effusion: elevation of both anterior and posterior fat pads are seen on lateral x-ray
• In an acute injury to the elbow, elevated posterior fat pad suggests the possibility of an intracapsular fracture
• Most common causes in children are supracondylar fracture, lateral epicondyle and separation of medial epicondylar ossification center
• Most common causes in adults are radial head or neck fractures, olecranon fractures, dislocations and fracture/dislocations
• Value of the posterior fat pad sign depends on its ability to predict an occult fracture in the absence of a radiographically visible fracture
• False-negative fat pad sign may occur if there is poor radiographic positioning, extracapsular abnormality or capsular rupture
• False-positive fat pad sign can be seen when the elbow is extended

References:

1. Goswami GK. The fat pad sign. Radiology 2002;222:419-420.

2. Skaggs DL, Mirzayan R. The posterior fat pad sign in association with occult fracture of the elbow in children. J Bone J Surg 1999;81:1429-1433.

Swirl Sign

An axial CT image of the brain in a trauma patient shows a hyperdense epidural hematoma (arrowheads) with a small rounded area of low attenuation (arrow) internally.

Facts: The Swirl Sign

• An area of low attenuation within the extra-axial hematoma, usually in epidural hematoma, seen on nonenhanced CT scan
• Represents an actively extravasating unclotted blood
• The area is surrounded by clotted blood (50-70 Hounsfield Units). Clotted blood is hyperdense on CT because of protein component of hemoglobin

Reference:

Al-Nakshabandi NA. The swirl sign. Radiology 2001; 218:433.

Left Atrial Enlargement

A frontal chest radiograph shows double density to the right of the spine (short arrows) and convex border of the left atrial appendage (long arrows).

A lateral view of the chest shows posterior displacement of the left mainstem bronchus by an enlarged left atrium (arrowheads).

Signs of Left Atrial Enlargement (LAE) on Chest Radiography

• Convex left atrial appendage
• Double density on the right side of the spine (one of the earliest signs)
• Double density on the left side as the left atrium extends into the left lower lobe
• Posterior displacement of the left mainstem bronchus posteriorly on lateral view, and superiorly on frontal view
• Spreading of the carina

Common Causes of LAE

• Acquired: mitral valve disease (stenosis or regurgitation), left ventricular failure, left atrial myxoma
• Congenital: VSD, PDA, hypoplastic left heart complex

Our case: severe mitral regurgitation

Reference:

Miller SW, Boxt LM, Abbara S. Cardiac Imaging the Requisites, 2009, 3rd edition.

C Sign of Talocalcaneal Coalition

Fig. 1: Lateral radiograph of the right ankle shows a C sign (yellow dotted line) that extends from the talar dome through the coalition component of the posterior talocalcaneal joint to the sustentaculum tali.
Fig. 2: Coronal reformatted CT image confirms the presence of talocalcaneal coalition (arrows) between the talus (T) and calcaneus (C).

Facts: Tarsal Coalition

• Abnormal bony, cartilaginous or fibrous articulation between two tarsal bones
• Congenital, caused by lack of bony segmentation
• Most common between calcaneus-talus and calcaneus-navicular
• Bilateral in 20% of cases

Imaging

• C sign seen on lateral view when middle facet talocalcaneal coalition is present (as in our case)
• Talar beak is an indirect sign of abnormal talonavicular motion, it is a bony spur from anterior superior aspect of talus
• CT is an excellent method to identify and characterize tarsal coalition

Reference:

Chew FS, Bui-Mansfield LT, Kline MJ. Musculoskeletal Imaging, 2003.

Pericardial Effusion - Oreo Cookie Sign

Figure 1: Lateral chest radiograph shows separation of the retrosternal (dark line parallel to the sternum anterior to the yellow star) and epicardial fat stripes (dark line behind the yellow star). This patient also has an anterior mediastinal mass due to lymphoma.
Figure 2: Axial contrast-enhanced CT image shows a large pericardial effusion (stars) separating the retrosternal fat stripe (double-headed arrow) and epicardial fat stripe (arrowheads).

Facts: Pericardium

• Pericardium has two layers: visceral (attached to myocardial surface and proximal great vessels) and parietal (free wall of pericardial sac)
• Pericardial sac normally contains 20-50 mL of fluid

Facts: Pericardial Effusion

• Most common cause = myocardial infarction with left heart failure
• Other causes: uremia, hypoalbuminemia, myxedema, infection, drug reaction, trauma, neoplasm, autoimmune disease
• Can be seen on radiography if volume exceeds 250 mL

Imaging Features

• PA or AP radiograph: water bottle-shaped morphology of the cardiomediastinal shadow
• Lateral view: separation of retrosternal and epicardial fat stripes by more than 2 mm (Oreo cookie sign)
• Oreo cookie sign: epicardial fat and retrosternal fat stripes = outer dark cookie layers; opaque fluid = white fluff of the cookie

Oreo cookies pictures

Reference:

Parker MS, Chasen MH, Paul N. Radiologic signs in thoracic imaging: case-based review and self-assessment module. AJR 2009;192:S34-S48.

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The Luftsichel Sign

A PA chest radiograph shows low left lung volume, haziness of the left lung with obliteration of the left heart border, a Luftsichel sign (arrowheads).
A lateral chest radiograph shows an anteriorly displaced left major fissure (arrows). The collapsed left upper lobe is up against the anterior chest wall.

Facts: Luftsichel sign

• Seen on PA chest radiograph of patients with left upper lobe collapse
• Paraaortic crescent of air with sharp margin extending anywhere from left apex to left superior pulmonary vein
• Luft = air; sichel = sickle [German]
• Caused by expansion of superior segment of left lower lobe due to left upper lobe collapse.
• In adults, it is an important clue to diagnose collapse that may be due to an obstructing endobronchial neoplasm.

Signs of Left Upper Lobe Collapse

• On PA view: Low left lung volume (elevated diaphragm), haziness of the left lung with obliteration of left heart border, elevated left hilum, near-horizontal course of the left main bronchus, Luftsichel sign
• On lateral view: Anteriorly displaced major fissure that parallels the anterior chest wall

Reference:

Blankenbaker DG. The Luftsichel sign. Radiology 1998;208:319-320.

Double Bubble Sign

Supine abdominal radiograph of a newborn presenting with billous vomiting shows a distended stomach and duodenal air bubbles "double bubble" sign. There is no gas distal to the duodenal bubble. Radiopaque materials overlying the right pelvis are due to soiled diaper.

Double Bubble Sign

• Radiographic signs describing two air-filled structures in the upper abdomen with little or no air distally
• Can be reproduced in upper GI study or ultrasound
• Left-sided bubble = stomach
• Right-sided bubble (usually right of midline) = duodenum
• Most common cause = duodenal atresia

Differential Diagnoses

• Intrinsic cause: duodenal atresia, duodenal stenosis, duodenal web
• Extrinsic cause: annular pancreas, malrotation with obstruction produced by midgut volvulus or by Ladd bands

Main Concern

• Must be differentiated from 'malrotation with obstruction (midgut volvulus)' because this condition requires urgent surgery
• Suspect midgut volvulus if stomach is distended but duodenum is normal or only slightly dilated

Reference:

Traubici J. The double bubble sign. Radiology 2001;220:463-464.

Seronegative Spondyloarthropathy (SNSA)

Figure 1: AP radiograph of the lumbosacral spine shows symmetric sclerosis and fusion (ankylosis) of the sacroiliac joints (red arrowheads). There is ossification of the outer fibers annulus fibrosus (arrows).
Figure 2: Lateral view of the spine of the same patient demonstrates ossification of the outer fibers of annulus fibrosus (arrows), squaring of anterior vertebral margin, and "shiny corner" sign (arrowhead).

Facts

• SNSA is a group of diseases that general pathology consists of negative rheumatoid factor (RF) and elevated erythrocyte sedimentation rate (ESR)
• Ankylosing spondylitis, reactive spondyloarthropathy, psoriatic spondyloarthropathy, spondyloarthropathy associated with inflammatory bowel disease, undifferentiated spondyloarthropathy
• Strong association with HLA-B27 haplotype
• Most common clinical presentation is low back pain (greater in the morning) and pathologic fracture

Imaging Findings

• First involves sacroiliac joints (erosion of synovial portion, then fusion in late stage), then thoracolumar junction and may involve whole spine
• Corner erosions of vertebral bodies produce "squaring" and reactive sclerosis produces "shiny corner" sign
• "Bamboo spine" caused by thin ossification of the outer fibers of annulus fibrosus at vertebral margin, common in ankylosing spondylitis

Key Differentiating Imaging Features

• Involvement of SI joints - rare in rheumatoid arthritis, normal in DISH, retinoid therapy
• Infection of SI joint typically unilateral

Our case: ankylosing spondylitis

Reference:

Ross, Brant-Zawadzki, Moore, et al. Diagnostic Imaging: Spine, 2004

"Vertebra Plana-Like" Lesion

Figs 1&2: Sagittal MR image (T1 post contrast) and coronal-reformatted CT image of the thoracic spine of a 14-year-old boy show complete collapse (arrows) of the mid thoracic vertebral body, preserved adjacent discs and enhancing soft tissues around the affected vertebral body extending into the epidural space (arrowheads).

Vertebra Plana

• Collapse of one vertebral body
• Normal adjacent intervertebral disks
• Height of the intervertebral space increased by at least 1/3 compared to normal
• Increased density of the collapsed vertebra

Etiology

• Strict criteria above apply to the diagnosis of eosinophilic granuloma, considered the most frequent benign lesion causing vertebra plana
• Other causes include: primary tumor (e.g. Ewing sarcoma, osteosarcoma, lymphoma), and metastasis, trauma and chronic osteomyelitis

Benign or Malignant?

• Clinical and radiographic course typically allows the physician to differentiate eosinophilic granuloma from other diagnoses that require diagnostic vertebral biopsy
• Using criteria based on studies of adult with compression fractures (differentiating benign from malignant compression fractures) may be helpful. The following MR findings were shown to be suggestive of malignancy: involvement of pedicle, irregular nodular paravertebral soft tissue lesion, marked and heterogeneous enhancement pattern.

Our case: metastatic round cell tumor to the spine causing "vertebra plana-like" appearance

References:
1. Baghaie M, Gillet P, Dondelinger RF, et al. Vertebra plana: benign or malignant lesion? Pediatr Radiol 1996;26:431-433.
2. Ippolito E, Farsetti P, Tudisco C. Vertebra plana. Long-term follow-up in five patients. J Bone Joint Surg Am 1984;66:1364-1368.
3. Shih TT, Huang K, Li Y. Solitary vertebral collapse: distinction between benign and malignant causes using MR patterns. J Magn Reson Imaging 1999;9:635-642.

Superscan

Figure: Bone scan image shows diffuse increased bone uptake throughout the skeleton with relative absence of kidney uptake (arrows), consistent with "superscan". There are several focal areas of uptake in the ribs, skull (arrowhead), scapulae and extremities indicating metastatic disease in a 73-year-old man with prostate cancer. The patient had a right craniotomy defect seen as a photopenic region on the posterior view.

Superscan "High ratio of bone uptake relative to soft tissue uptake, absent or relatively decreased renal uptake, homogeneous uptake of axial skeleton"

Two Types of Super Scan

1. Metabolic: homogeneous uptake, usually hot at the calvarium, uptake seen at the extremities
2. Metastatic: heterogeneous, usually absent uptake at the calvarium (unless metastatic lesions), uptake at distal extremities usually not seen

Metastatic "Superscan"

• Prostate cancer, breast cancer, lung cancer
• RCC, lymphoma, bladder cancer

Reference:

Morton K, et al. Diagnostic Imaging: Nuclear Medicine. Amirsys, Inc. 2007

Thickened Gallbladder Wall

Fig. 1: Transverse ultrasound image of the gallbladder in a 79-year-old afebrile woman with RUQ pain. There is diffuse gallbladder wall thickening (6 mm) and a hyperechoic material (arrow) in the gallbladder lumen. The gallbladder is distended.
Fig. 2: Longitudinal US image shows acoustic shadowing casted from hyperechoic material, representing a gallstone.

Differential Diagnosis of Thickened Gallbladder Wall

1. Gallbladder disease - cholecystitis (acute or chronic)
2. Liver disease - hepatitis, cirrhosis
3. Diffuse disease - hypoalbuminemia, heart failure, renal failure

Our case was a surgically proven acute calculous cholecystitis.

Reference:
Chapman S and Nakielny R. Aid to radiological differential diagnosis. 4th ed.

Double PCL Sign

Fig: Sagittal PD image of the knee shows 'double PCL sign'. Note the 'extra' dark band (arrows) beneath the true posterior cruciate ligament (arrowheads). This dark band represents 'bucket-handle tear of meniscus'. Joint effusion is marked by a red star.

Double PCL Sign

• Displaced fragment of meniscus in the intercondylar notch of the knee, resembling two posterior cruciate ligaments (PCL)
• Sign of bucket-handle meniscal tear
• Usually tear occurs in young active person
• Medial meniscus > lateral meniscus
• Confirmation on coronal image that shows displaced fragment in the notch
• Look for concomitant chronic ACL tear
  

Reference:
Stoller DW, et al. Diagnostic imaging: orthopedics. 2004

Crazy-Paving Pattern

Fig. Axial CT of the chest shows diffuse bilateral ground-glass opacities superimposed by interlobular septal thickening (arrowheads) and intralobular lines (blue arrows). Note a left chest tube used to treat left pneumothorax, which brought this patient to the hospital.

What is "Crazy-Paving" Pattern?

• Ground-glass opacity superimposed with interlobular septal thickening and intralobular lines
  
• Can be scattered or diffuse
  
• Can be caused by alveolar filling process, interstitial process, or a combination

What Can Cause "Crazy-Paving" Pattern?

• CLASSIC: Pulmonary alveolar proteinosis 
  
• COMMON: Pneumocystis jirovecii pneumonia (PCP), pulmonary edema (ARDS), pulmonary hemorrhage
  
• NOT COMMON: Bronchioloalveolar carcinoma, alveolar sarcoidosis, nonspecific interstitial pneumonitis (NSIP), Cryptogenic organizing pneumonia (COP), lipoid pneumonia
  

Our case is a patient with biopsy proven pulmonary alveolar proteinosis.

Reference:

1. Rossi SE, et al. "Crazy-Paving" Pattern at Thin-Section CT of the Lungs: Radiologic-Pathologic Overview. Radiographics 2003;23:1509.

2. Johkoh T, et al. Crazy-paving Appearance at Thin-Section CT: Spectrum of Disease and Pathologic Findings. Radiology 1999;211:155.

Who is Aunt Minnie?

Beside 'Aunt Minnie' as a popular radiology website, do you know who really is Aunt Minnie?

A few communications in Radiology and AJR provided the answer.

Aunt Minnie

• Constellation of observations virtually pathognomonic of an entity (usually of an unusual or unexpected disease)
• Subliminal or subconscious pattern recognition of disease (similar to recognizing Aunt Minnie among a large group of similar women)
• The term attributed to two figures in radiology history: Ed Neuhauser (previous Chief at Children Hospital Boston) and Ben Felson (neither had an aunt named Minnie)

Reference:
Hall, et al. Gestalt: Radiology's Aunt Minnie. AJR 2008 (October)

Image source: www.auntminnie.com

Colon Cutoff Sign

Fig. 1: Supine abdominal radiograph in a 30-year-old man with acute abdominal pain shows gas in the transverse colon (C) with an abrupt termination at the level of splenic flexure (arrowheads). The more distal colon is decompressed. S = stomach
Fig. 2: Axial CT image of the same patient (done a few hrs later) shows extensive inflammation and necrosis of the pancreas (arrows) with free fluid in the abdomen (stars).

What is Colon Cutoff Sign?
Abrupt termination of gas in proximal colon at the level of the splenic flexure.
Applied to radiography, CT and contrast enema studies

What Can Cause Colon Cutoff Sign?

• Most common = acute pancreatitis
• True colonic obstruction e.g. colonic malignancy
• Other causes of colonic inflammation

Why Does It Occur?
In acute pancreatitis, inflammatory exudates in retroperitoneal space extend into 'phrenicocolic ligament' causing spasm of the splenic flexure wherer the colon returns to retroperitoneum. (Remember - transverse colon in peritoneal cavity, descending colon in retroperitoneum, phrenicocolic ligament is a transition point where transverse and descendinc colon is separated)

Available in Podcast (Thai language only): website | iTunes

Reference:
Pickhardt P. The colon cutoff sign. Radiology 2000;215:387.

Air-Fluid Levels at Different Heights in the Same Loop of Bowel

Upright abdominal radiograph of the same patient shows multiple air-fluid levels in the small bowel. Note 'different heights of air-fluid levels in the same loop' (arrows). SB = small bowel, C = colon.

Differential Air-Fluid Levels

• Two distinct air-fluid interfaces on an upright abdominal radiograph that are at different heights but within the same loop of bowel.
• Once believed to be strongly suggestive of mechanical small bowel obstruction (due to ongoing peristalsis against mechanical blockage BUT it can be found in both mechanical obstruction and ileus (in one series, 50% of mechanical obstruction and 29% of ileus)
  
• Helpful to suggest mechanical small bowel obstruction if a differential air-fluid level is 2 cm or greater (however, not the other way around!) with a reasonable positive predictive value (PPV). As height increases, PPV and specificity increases.
• Differential height of 2.5 cm or greater is suggestive of high-grade small bowel obstruction.

This case: partial, low-grade small bowel obstruction, likely due to adhesion (history of multiple previous abdominal surgery).

Reference:
1. Harlow CL, et al. Diagnosis of bowel obstruction on plain abdominal radiographs: significance of air-fluid levels at different heights in the same loop of bowel. AJR Am J Roentgenol 1993;161:291.
2. Lappas JC, et al. Abdominal radiography findings in small bowel obstruction: relevance to triage for additional diagnostic imaging. AJR Am J Roentgenol 2001;176:167.