If you guessed pneumothoax, you are correct!

The fourth picture on the previous page is the "lung point sign," which is pathognomic for pneumothorax under the ultrasound probe. It reflects the movement of the partially filled lung coming into and out of view as it makes contact with the parietal (chest wall) pleura.

Interestingly, the use of ultrasound to detect a pneumothorax was first studied by a veterinarian, Dr. Ratanen, in 1986. The first human studies were performed by Wernecke, et.al. in 1987, and since then ultrasound been used increasingly in medicine for detecting pneumothorax.

Wernecke's original research was followed by Dr. D. Lichtenstein et.al. in the 1990’s, who primarily studied pulmonary ultrasound in intensive care patients. Since initial studies were completed, a significant amount of additional research has supported the use of ultrasound for the diagnosis of pneumothorax and has found that in the hands of a moderately trained sonographer is universally more sensitive for PTX than chest radiography (CXR). Kirkpatrick, et. al. have noted that upwards of 60% of PTX are missed on conventional CXR.

Selected recent studies examining ultrasound (US) for pneumothorax (PTX) have found the following:

Italian Study by Garofalo, (Jun 2006, Radiologica Medica) -- In 46 patients with pneumothorax (PTX) after percutaneous needle biopsy, detection of PTX by US was 95.6% sensitive and 100% specific, whereas CXR detected only 19 of 46 PTX.

American study by Blaivas (2005, Acad Emerg Med)--176 trauma patients, 53 with PTX confirmed by CT. US sensitivity was 98.1% and specificity 99.2%, XRAY sensitivity 76%, specificity 100%. US allowed sonologists to differentiate between small med and large PTXs with reasonable agreement with CT results.

While the presence of lung sliding has been found in several studies to rule out a pneumothoax, absence of lung sliding is highly suggestive of pneumothorax. Moreover, presence of comet tails is a good indicator of an inflated lung; however, absence of comet tails is not indicative of PTX.

In Lichtenstein's study, it was found that the absence of comet-tail artifact had a sensitivity and negative predictive value of 100% and a specificity of 60% for the diagnosis of pneumothorax. Again, a pneumothorax can be nearly excluded if comet-tail artifact is seen. Lastly, the lung point sign, as seen in our case, had a sensitivity of 66% and a specificity of 100% in the study.

Pitfalls in US for PTX:
Certain conditions are well described to produce false positives in diagnosing PTX with US. These include but are not limited to:
-Patients with COPD (see study by Slater in Chest, March 2006). "COPD patients more difficult to detect PTX, and may need other imaging."
-Patients with lung blebs
-Patients with large lung contusions which distort the pleura
-Patients with subcutaneous emphysema (which should be evident to the sonographer as a more shallow interference than at the pleural level)

Start practicing, grab me for help and good luck!

Also, please refer to the excellent LMS lecture on "Pulmonary Ultrasound" created by Drs. Cook and Hunt here (contact me for a password).

Thanks for looking!

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