December 30, 2010


Plain abdominal radiograph shows multiple tiny stones (arrows) lined in the distal right ureter. The patient has had a recent extracorporeal lithotripsy.

Facts: Steinstrasse
  • Steinstrasse is a German word, meaning "stone street" or "street of stones" first coined by the German pioneer of lithotripsy
  • After lithotripsy, tiny stones line up in the ureter producing an appearance resembling a cobbled street on plain radiograph
  • Steinstrasse can develop in 1 day to 3 months after stone fragmentation. It can develop after the first ESWL, or after several sessions.
  • Incidence increases with stone size
  • Most common location = distal ureter, followed up upper ureter
  • It often passes by itself. 25% of patients, however, may experience obstruction at the ureteral level. If obstructed, percutaneous drainage or ureteral stent placement may be needed to manage ureteral obstruction until the fragments become dislodged and pass
  • Steinstrasse best detected with plain radiography
  • Ultrasound is the most appropriate imaging mean to detect associated obstruction (hydronephrosis)

1. Zagoria RJ. Genitourinary Radiology The Requisites, 2nd edition.
2. Sayed MA, El-Taher AM, Aboul-Ella HA, Shaker SE. Steinstrasse after extracorporeal shockwave lithotripsy: aetiology, prevention and management. BJUI 2001; 88:675-678.

December 27, 2010

ILO International Classification of Radiographs of Pneumoconioses (1)

PA chest radiograph of an 80-year-old man who was a miner decades ago shows multiple large opacities (arrows, large opacity = parenchymal opacity greater than 1 cm) and several tiny rounded opacities in the right lower and left mid/lower lung zones. With the history of exposure, adequate lag time and chest radiographic findings, the patient has findings consistent with coal worker pneumoconiosis.

Background: ILO
  • ILO (International Labour Office, based in Geneva) produces guidelines on how to classify chest radiographs of persons with pneumoconioses
  • The guidelines aim to standardize classification and facilitate comparisons of data internationally
  • The last ILO revision of this classification was in 2000, it is specific for postero-anterior (PA) chest radiography only
  • Because interpreting chest radiography for pneumoconiosis has shown an unacceptable variability, the US's National Institute for Occupational Safety and Health (NIOSH) began the "B" reader program in 1978. The "B" reader has to pass the certification examination organized by NIOSH.
  • It is important to note that there is no pathognomonic imaging sign of pneumoconioses*. Diagnosis requires a combination (2 out of 3) of history of exposure, radiographic findings and pathological findings.
  • Based on ILO classification, these informations on PA chest radiographs are required for reporting: technical quality of the film, parenchymal abnormalities, pleural abnormalities, symbols (findings other than that of pneumoconiosis) and comments.
  • Parenchymal opacities are divided into small and large opacities. Small opacities can be rounded or irregular. These are further subdivided based on their size
  • Pleural abnormalities can be focal plaque, costophrenic angle obliteration and diffuse pleural thickening
1. ILO. Guidelines for the use of the ILO international classification of radiographs of pneumoconioses, revised edition 2000.
2. Wikipedia. "B" reader.

December 24, 2010

Thymic Involution

Axial CT image shows a normal-appearing thymus (arrows) with minimal soft tissue strands and mostly fat replacement of the gland. The gland has concaved margins.

Facts: Thymic Involution
  • Thymus undergoes a gradual loss of cortical lymphotcytes and atrophy of epithelial cells and replacement by fat
  • Believed to start at puberty but new data suggest that it actually starts from the first few years of life
  • By the age of 40 to 45 years, more than 50% of thymus is replaced by adipose tissue
  • Speed of involution increased with stress and other factors
  • Normal/involuted thymus: normal-shaped, flat or concaved margin, fat replacement increases with age and by the age of 40 the thymus is usually mostly fatty
  • Thymic hyperplasia: convex margin, diffusely enlarged gland but normal shape, homogeneous attenuation similar to normal thymic tissue
  • Thymoma: homogeneous, well-defined soft tissue mass, calcification, homogeneous enhancement
Our case-- thymic involution in a patient with myasthenia gravis, confirmed at surgery.

1. Bogot NR, Quint LE. Imaging of thymic disorders. Cancer Imaging 2005; 5:139-149.
2. Greer JP, et al. Wintrobe's Clinical Hematology, 12th ed, 2009.

December 21, 2010

Dual Energy CT (2)

One Basic Reason for Use of Dual Energy CT: Material Differentiation

  • By scanning a patient at two different energy spectra (on an example above, at 56 kV and 76 kV), the attenuation difference of the same material is different.
  • Iodine has higher attenuation difference, compared to bone
  • With this nature, scanning allows the computer to process bone and iodine content on images differently.
Routine Use of Dual-energy CT for Material Differentiation
  • Creation of 3D vascular images ("Direct Angio") by easy removal of bony structures
  • Plaque analysis (calcified vs. soft plaques)
  • Lung perfusion
  • Virtual unenhanced scan (creation of unenhanced scan from enhanced images by deleting iodine content from the images)
  • Calculi characterization (uric acid vs. others)

Reference: Fletcher JG, Takahashi N, Hartman R, et al. Dual-energy and dual-source CT: is there a role in the abdomen and pelvis? Radiol Clin N Am 2009; 47:41-57.

December 18, 2010

Dual Energy CT (1)

A Growing Need for a New Kind of CT
  • We need a better delineation of tissue components than just simple Hounsfield Units
  • We need to scan faster to image the beating heart (decrease temporal resolution), esp. in cases with high heart rate, irregular heart rate
What Is Dual Energy CT?
  • CT that uses the data of two different energy spectra to display anatomy and physiology (regular CT scans utilize one energy spectrum to create images)
  • Dual-source CT describes CT that has two x-ray sources and two detectors mounted on a single gantry. The x-ray sources can produce two different energy spectra, or one spectrum. Dual-source CT can run in either dual- or single-energy mode
What Are Possible Hardware Configurations for Dual Energy CT?
  • Two x-ray sources (dual-source CT)
  • Rapid kV switching (single-source CT)
  • Sandwich detector CT (two layers of detectors detecting x-rays at different energy spectra)
Image credit:

Fletcher JG, Takahashi N, Hartman R, et al. Dual-energy and dual-source CT: is there a role in the abdomen and pelvis? Radiol Clin N Am 2009; 47:41-57.

December 15, 2010

Non Accidental Injury (NAI): Rib Fractures

Chest radiography of a 2-month-old baby shows multiple bilateral rib fractures of different ages. Left-sided rib fractures (arrowheads) appear to have callus formation, while the right sided fractures (arrows) do not. Note right pleural effusion/thickening laterally.

Facts: Fractures in Non-Accidental Injury
  • Second most common findings of child abuse after dermatologic findings (bruises, contusions, burns)
  • Can be found throughout the whole skeleton
  • Likely multiple and in diverse stages of healing
  • Long bone fractures are the most common, with some oblique or spiral components (due to torsion force)
  • Classic metaphyseal lesions and location of fractures (ie, posterior rib fractures) are more suspicious than others
Rib Fractures in NAI
  • Highly predictive of child abuse in the absence of accidental trauma or certain skeletal diseases (e.g., osteogenesis imperfecta), particularly in children less than 3 years old
  • In children with rib fractures, the likelihood of NAI decreases with increasing age
  • Multiple rib fractures are more likely to be seen in NAI compared to single fractures
  • NAI is more likely in the presence of posterior rib fracture
Our case: non-accidental injury with multiple rib fractures in various stages of healing

Medina LS, Applegate KE, Blackmore CC. Evidence-based Imaging in Pediatrics, 2010.

December 12, 2010

Hepatic Portal Venous Gas

An abdominal radiograph shows diffuse distention of the small bowel, relative paucity of colonic gas and hepatic portal venous gas at the corner of the image.

  • Rare condition occurring when intraluminal gas and/or gas produced by intestinal bacteria enters the portal venous circulation
  • Initially thought to be an ominous sign with an estimated mortality of 75%-80% (more recently, mortality rates are 25%-35%)
  • Main factors that allow development of portal venous gas: intestinal wall alteration, bowel distention, ischemia and sepsis
  • Most common = intestinal ischemia with or without documented mesenteric thrombosis, necrotizing enterocolitis (NEC)
  • Others = C.difficile colitis, peptic ulcer disease, gastric cancer, diverticulitis, abdominal trauma, intra-abdominal abscess, inflammatory bowel disease
  • Iatrogenic = complications of endoscopic and radiological procedures
  • Diagnosis can be made by abdominal x-ray or ultrasound, but CT is the gold standard
  • Branching lucencies extending to within 2 cm of the liver capsule (predominantly in the anterior-superior aspect of the left lobe)
  • On US, it appears as echogenic particles flowing within the portal vein

Our case - patient with sepsis, severe ischemic/infarcted colitis and end-staged pancreatic cancer

Alqahtani S, Coffin CS, Burak K, et al. Hepatic portal venous gas: a report of two cases and a review of the epidemiology, pathogenesis, diagnosis and approach to management. Can J Gastroenterol 2007; 21:309.

December 9, 2010

Infantile Hypertrophic Pyloric Stenosis

Longitudinal scan of the stomach (as labeled) shows a thickened (5 mm) wall of the pylorus and elongation of the pyloric canal. Labe

Facts: Pyloric Stenosis
  • Most common surgical etiology for young infant presenting emergently with nonbillous vomiting
  • Incidence: 2 to 5 of every 1,000 infants
  • Multifactorial etiology: genetic, biochemical and environmental association
  • Hypertrophy of the pyloric muscle, leading to gastric outlet obstruction (vomiting, dehydration, poor weight gain and hypochloremic metabolic alkalosis)
  • Average age of presentation = 3 weeks old (rare before 1 week, or after 3-4 months)
  • US is now the imaging modality of choice for diagnosis of this condition. It can directly show the pyloric muscle
  • Elongation of the pyloric canal
  • Persistent spasm of pyloric canal with little, if any, fluid passing into the duodenum
  • Persistent thickening of the circular muscle in the canal
  • Pyloric muscle thickness (one wall) greater than 4 mm, or pyloric length greater than 16 mm (cutoff values vary depending on the sensitivity, specificity needed to make the diagnosis)
  • Imaging differential diagnosis is pylorospasm. In pylorospasm, there is usually no thickening of the pylorus (can be up to 2-3 mm) and when visualized in real time the pylorus can open
  • If ultrasound is negative, UGI series or nuclear medicine to evaluate for reflux may be necessary.
1. Swischuk LE. Imaging of the newborn, infant and young child, 5th edition.
2. Hernanz-Schulman M, Berch BR, Neblett WW. Imaging of infantile hypertrophic pyloric stenosis (IHPS). Evidence-based Imaging in Pediatrics 2010; 5:447-457.

December 6, 2010

Peritoneal Sarcomatosis

Axial CT image of the abdomen shows soft-tissue implants and omental caking (arrows) with small ascites.

Peritoneal Surface Malignancy
  • Carcinomatosis
  • Lymphomatosis
  • Sarcomatosis
  • Mesothelioma
  • Desmoplastic small round cell tumor
Peritoneal Sarcomatosis
  • Disseminated intraperitoneal spread of sarcoma in the absence of significant extraabdominal sites of disease
  • Rare disease.
  • Most commonly due to GI stromal tumor (GIST), liposarcoma and leiomyosarcoma

Imaging Findings
  • Similar to other peritoneal surface malignancy: soft-tissue implants along peritoneum and omentum
  • Often hypervascular, and with variable amount of ascites (differ from other peritoneal surface tumors)
Our case: Sarcomatosis due to GIST. Ascites is believed to be due to treatment with imatinib

Oei TN, Jagannathan JP, Ramaiya N, Ros PR. Peritoneal sarcomatosis versus peritoneal carcinomatosis: imaging findings at MDCT. AJR 2010; 195:W229-W235.

December 3, 2010

Image Wisely Campaign Launched

Image Wisely is a campaign to encourage imaging providers to
  • Optimize imaging examinations to use only the radiation necessary to produce diagnostic quality images
  • Convey messages to the imaging team to ensure that the facility optimizes its use of radiation when imaging patients
  • Communicate optimal patient imaging strategies to referring physicians, and be available for consultation
  • Routinely review imaging protocols to ensure the use of the least amount of radiation necessary to acquire a diagnostic quality image for each exam
Image Wisely is a collaborative initiative of the ACR, RSNA, ASRT and AAPM
Imagine Wisely campaign initially focuses on CT

More information: