Tag Archives: anatomy

Hepatization versus Pseudo-Hepatization

Counter-intuitively, when insonating the lungs of healthy patients, we don’t “see” lung tissue. Instead we see and interpret artifacts arising from the pleural lines and the diaphragm.  These artifacts change with pulmonary disease processes.  In pneumonia, the airway spaces become inspissated with bacterial byproducts and consequently the sonographic appearance of lung tissue changes.

The transformation of lung tissue is termed hepatization: the lung tissue now appears similar to liver tissue.

This can be confusing in the lower lung fields, especially adjacent to the diaphragm because we use the mirror image artifact of the liver and spleen to indicate that lung tissue is normal. This mirrored, artifactual splenic or liver appearance could then be called pseudo-hepatization.

 

 

So, how do we differentiate hepatized lung versus pseudo-hepatized lung?

  1. Never use a single image for your diagnosis, scan through area and convince yourself (then save a representative image or clip for QA).
  2. Be systematic and scan down from the lung apices to the diaphragm.
  3. Hunt for the diaphragm and use it as a dividing line between the lung and the abdominal organs.
  4. Hepatized lung will often have a rim of fluid around it.

Image 1: Normal lung with visible diaphragm

Ultrasound of lung and spleen from Sinai EM Ultrasound on Vimeo.

Image 2: Normal lung with obscured diaphragm

Lung and Spleen Interface on ultrasound from Sinai EM Ultrasound on Vimeo.

Image 3: Hepatized lung at the lower lung field

What the Heck 2

This patient presented with diffuse abdominal pain, tachycardia, and peritonitis on physical examination. A FAST exam was performed to assess for free intraperitoneal fluid, and the following view of was obtained transversely in the pelvis.

First, just look at the still image and make your best guess. Then press play:

Did the large anechoic structure in the near field look like the bladder? Or was it the anechoic area in the far field? The operator was thrown off a bit by the complex echoes within the anterior structure. Remember the bladder is going to conform to the shape of the pelvis as it enlarges, so it will take on a characteristic square/trapezoidal shape in transverse orientation. But for the same reasons free fluid will take the same shape. Through the sweep from cranial to caudal you’ll notice two fluid collections; the anterior one seemed to have much more internal echo and debris. Don’t assume that’s the peritoneal fluid- urine can also look that way.

This was the sample obtained when a Foley catheter was inserted into the bladder:

UTI 500x380 What the Heck 2This definitely looked (and smelled) better sonographically.

Here is the longitudinal (sagittal) view through the pelvis:

As usual, the sagittal view gives a better overview of the anatomy of the pelvis. When using the transverse view of the pelvis, you can miss small amounts of pelvic fluid more easily, confuse fluid collections for the bladder, and make incorrect assumptions. Just more support for the sonographic dogma of imaging everything in two planes.

Case resolution:

CT scan confirmed free intraperitoneal fluid but no free air or other signs of bowel perforation. The hemoglobin was stable through several assessments. The patient had an obvious urinary tract infection and renal failure on laboratory evaluation. Thus the fluid was thought to be new onset of ascites in the setting of urosepsis and mult-organ dysfunction.

Tips:

  • Always image anatomy in at least two planes, and fan through anything that isn’t moving.
  • Rethink assumptions when the anatomy doesn’t look as it should. For example, an oddly-shaped or highly echoic bladder may not be bladder at all, or it might just be an abnormal bladder.
  • ALWAYS clean the machine and put it back where you found it when you are done.

I had to throw that in there, sorry.

 

Lung Ultrasound Pitfalls

US lung consolidation Tsung 500x514 Lung Ultrasound PitfallsThoracic sonography is one of the most rapidly growing areas of emergency and critical care ultrasound. One very important emerging indication is to assess for lung consolidation. The characteristic appearance of consolidated lung is very sensitive and specific for pneumonia, but novices should heed some important pitfalls in making the diagnosis.

Special thanks to Jim Tsung, MD, MPH and Brittany Jones, MD for their tips, videos, and ongoing research in this important field! For further reading on this topic, please see this article.

Pitfall #1 – confusing thymus for a consolidation

Normal thymus in sagittal view:

Thymus (top half of screen) and heart (bottom right). Don’t confuse thymus for lung consolidation. Note there are no air bronchograms, but thymus has a faint speckled appearance.

Normal thymus in transverse view:

Thymus (top half of screen) and heart (bottom right). Don’t confuse thymus for lung consolidation. Note there are no air bronchograms, but thymus has a faint speckled appearance
Pneumonia adjacent to Thymus in transverse view:

Lung consolidation with air bronchograms (top left) adjacent to normal thymus (speckled appearance on top right) with heart (bottom right)

Pitfall #2 – mistaking spleen for consolidation.

This is an important pitfall for everyone to know about. The same issue applies to the liver & stomach. The sensitivity of lung US for pneumonia rises >90% if this mistake is avoided.

Left lower chest- sagittal view:

Be careful scanning the left lower chest (left anterior and left axillary line) – air in stomach and spleen may look like pneumonia if you don’t realize that you have scanned inferior to the diaphragm and past the end of the pleural line. Most common error by novices.

Left lower chest- transverse view:

Be careful scanning the left lower chest (left anterior and left axillary line) – air in stomach and spleen may look like pneumonia if you don’t realize that you have scanned inferior to the diaphragm and past the end of the pleural line.

Pitfall #3- missing pleural effusion

Here are a few examples to refresh your memory.

Left pleural effusion:

Identify:

  • Pleural effusion (anechoic wedge just beneath ribs and pleura)
  • Lung
  • Diaphragm
  • Spleen
  • Air in stomach

Do not confuse spleen and air in stomach for pneumonia.

Right pleural effusion:

Identify:

  • Pleural effusion
  • Lung
  • Diaphragm
  • Liver

Arcuate Vessels

Arcuate vessels are commonly seen on ultrasound evaluation of the uterus. Occasionally they can be confused with subchorionic hemorrhage, ovaries, and other structures so it’s worth looking at their characteristic appearance.

Once again, thanks to Dr. Gray for his lovely, copyright-free images:

Gray589 500x296 Arcuate Vessels

Here we see the Uterine venous plexus giving rise to the helicine branches, aka arcuate vessels. They run circumstantially through the outer margin of the myometrium.

In the images below, anechoic areas are visible in the posterior aspect of the myometrium (arrows in top two images). The bottom two images reveal the same structures with and without color flow, demonstrating their vascularity. These vessels are normal anatomic variations, and can become more engorged during pregnancy as uterine bloodflow increases.

 

This is again visible posteriorly in this video of a gravid uterus:

 

Pupillary Light Reflex

We’ve all seen ultrasound augment the physical examination and even allow for assessments we could not otherwise accomplish at the bedside. One great example is the use of ultrasound to check the pupillary light reflex. If you are wondering why a pen light would not suffice for this physical examination standby, you have never encountered a patient with facial trauma whose eyes were swollen shut.

We already know what to look for without ultrasound (thanks to Greyson Orlando and Wikipedia for the GIF):

Eye dilate thumb 300px Pupillary Light ReflexBy directing the beam of a high-frequency linear array transducer through the plane of the iris, you can obtain the following image (while shining a light through the closed eyelid of the same or contralateral eye):

It takes a bit of practice to align both planes, and not worth the trouble if the patient can open their eyes.

Placing a Tegaderm over the closed eye prior to applying gel can make cleanup much easier afterwards (a useful tip for any type of ocular ultrasound).

Further reading:

  • Sargsyan AE, Hamilton DR, Melton SL, et al. Ultrasonic evaluation of pupillary light reflex. Critical Ultrasound Journal. 2009 1(2): 53-57.
  • Harries A, Shah S, Teismann N, Price D, Nagdev A. Ultrasound assessment of extraocular movements and pupillary light reflex in ocular trauma. Am J Emerg Med. 2010 Oct; 28(8):956-9.

Lung point

Thoracic ultrasound is one of the hottest topics in emergency and critical care sononography. Assessment for pneumothorax is accurate and relatively easy to learn.

One important sign when assessing for pneumothorax is the lung point. This is the point where normal pleural interface contacts the boundary of the pneumothorax. It is the most specific sign for pneumothorax using ultrasound.

Using B-mode ultrasound, the lung point will appear as the boundary between normal lung sliding and still lung.

Lung point:

Continue reading