Sternal Osteomyelitis

Chest radiograph of a patient who had sternal pain, fever and discharge shows no obvious bony abnormality.

Sagittal STIR and coronal T1W MR images demonstrate bone marrow edema with soft tissue changes in the sternum and right sternoclavicular joint (arrows). 

Facts:

• Uncommon infection of the sternum and sternoclavicular joint
• Usually affecting drug addicts, individuals with history of recent subclavian catheter placement, and patients with chronic debilitating illnesses
• Inciting organisms vary widely depending on demographics
• High failure rates of medical treatment alone. Typical treatment includes surgical debridement and en bloc removal

Imaging

• Radiograph is rarely helpful
• CT may show bone destruction but this may be late because damage begins in the joint. Surrounding soft tissue abnormalities are often a useful sign.
• MRI much more sensitive to detect joint and bone changes that are similar in findings to other areas of bone/joint infection

Reference: 

Shields TW et al. General Thoracic Surgery, 7th edition, 2009.

Renal Ultrasound for Elevated Serum Creatinine

A sagittal ultrasound image of the right kidney shows a normal-sized kidney with normal parenchymal echogenicity in a patient with acute renal failure. 

What clinicians want to know is whether elevated serum creatinine "acute or chronic" 

• This information is important to narrow differential diagnosis, urgency of investigation and treatment. 
• Chronicity of renal dysfunction can be determined with 1) a search for previous measures of renal function (i.e., old labs), 2) clinical history (i.e., recent onset of acute illness, oliguria that would suggest acute renal failure), 3) daily deterioration of renal function (suggestive of acute renal failure - ARF), 4) ultrasound
• ARF can be prerenal, renal or postrenal

Why Ultrasound?

• Ultrasound can help determining the kidney size. Small renal size (less than 8 cm in adults) is suggestive of CRF
• Demonstrate hydronephrosis, suggesting a postrenal cause. Note that to produce ARF, both kidneys must be affected (i.e., bilateral ureteric obstruction or bladder outlet obstruction, or hydronephrosis of a single functioning kidney)
• To exclude obstruction, US should be done as early as possible. But US is not necessary if there are "clear reversible causes on initial assessment + Rx instituted + clear evidence of prompt response with return to normal renal function within a few days"
• Increased echogenicity of renal cortex is not a sensitive measure of renal function. When present, it is more commonly seen in tubulointerstitial disease rather than glomerular disease

Limitations of Ultrasound

• No hydronephrosis is not equal to no obstruction. False negative study can occur 1) in the first few days of obstruction because the collecting system is relatively noncompliant, 2) if ureters and collecting systems are encased by tumor or fibrosis
• Detection of hydronephrosis can be difficult in patients with cystic kidney disease

Reference:

Baxter GM, Sidhu PS. Ultrasound of the urogenital system, 2006.

Gallbladder Cholesterolosis

Longitudinal US image of the gallbladder demonstrates multiple tiny echogenic spots within the wall with comet-tail artifacts. No evidence of gallbladder wall thickening. 

Facts:

• Other names: cholesteatosis, strawberry gallbladder
• Common, degenerative, proliferative changes of gallbladder
• Usually in females during their 4th and 5th decades
• Usually asymptomatic
• Not associated with increased risk of malignancy, cholelithiasis or cholecystitis

Differentiation from Adenomyomatosis:

• May be difficult at times because they may coexist and are believed to be a continuum of same pathology
• In cholesterolosis, the gallbladder has normal size, shape, lumen and often normal wall thickness

Reference:

Schmidt G. Differential diagnosis in  ultrasound imaging: A teaching file, 2006