Steinstrasse

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

Imaging

• Steinstrasse best detected with plain radiography
• Ultrasound is the most appropriate imaging mean to detect associated obstruction (hydronephrosis)

References:

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.

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.

Classification

• 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

References:

1. ILO. Guidelines for the use of the ILO international classification of radiographs of pneumoconioses, revised edition 2000.

2. Wikipedia. "B" reader.

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

Imaging

• 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.

Reference:

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.

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.

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: medical.siemens.com

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.