Welcome to another ultrasound-based case, part of the “Ultrasound For The Win!” (#US4TW) Case Series. In this case series, we focus on a real clinical case where point-of-care ultrasound changed the management of a patient’s care or aided in the diagnosis. In this case, a 46-year-old man with a history of alcohol abuse presents with diffuse abdominal pain.
A 46-year-old man presents to the Emergency Department (ED) for evaluation of severe generalized abdominal pain. His past medical history includes peptic ulcer disease (PUD) and alcohol abuse. He reports dull epigastric abdominal pain for 2 days, acutely worsening and becoming more diffuse prior to arrival in the ED. He acknowledges drinking more heavily and taking high doses of NSAIDs in an attempt to “ease the pain”. He has associated nausea and anorexia, but denies vomiting or change in bowel movements. He denies any history of trauma or a history of prior abdominal surgeries. His review of systems is otherwise non-contributive.
- BP 96/55 mmHg
- P 118 bpm
- RR 25 breaths/min
- O2 96% room air
- T 36.2 C
- Abdominal aortic aneurysm (AAA)
- Acute cholecystitis
- Peptic ulcer disease (PUD)
- Perforated viscus
- Renal colic
- Small bowel obstruction
On physical examination, you examine a middle-aged man who appears to be in significant pain, curled in the stretcher and clutching his abdomen. He appears pale and diaphoretic. On auscultation his heart is tachycardic with no murmurs, and lungs are clear bilaterally. His abdominal examination reveals diffuse tenderness to palpation with guarding.
Given the concern for an acutely ill patient with severe generalized abdominal pain, you perform a point-of-care ultrasound while investigations including laboratory tests and a bolus of normal saline and analgesia are given. With the patient laying supine, you visualize a normal diameter abdominal aorta with no aneurysm. However, on the right upper quadrant view you visualize the following:
Given the concern for pneumoperitoneum from a perforated viscus, aggressive fluid resuscitation and broad-spectrum antibiotics are started and general surgery is emergently consulted.
Ultrasound Image Quality Assurance (QA)
The point-of-care ultrasound images of the right upper quadrant reveal the classic sonographic findings of pneumoperitoneum. Although the curvilinear probe is being used, the linear probe can also be used which can increase the sensitivity to detect pneumoperitoneum given its higher resolution.1 Note that the free fluid visualized in Morison’s Pouch appears echogenic with debris [Fig. 1, Fig. 2]. This ‘dirty free fluid’ can often be found with a perforated viscus.
The Shifting Phenomenon
The images from this case highlight the utility of using patient positioning to your advantage with bedside ultrasound studies in order to improve diagnostic accuracy. Figure 1 shows a view of the right upper quadrant with the patient supine, revealing free fluid in Morison’s Pouch. When the patient is shifted to the left lateral decubitus position [Fig. 3], the area between the left hepatic lobe and abdominal wall is interrogated for extraluminal air, which will track to the least dependent (‘anti-dependent’) area. This is referred to as the “shifting phenomenon.”2,3
The key to identifying pneumoperitoneum with ultrasound is the identification of artifacts that are indicative of air, and finding these artifacts where air shouldn’t normally be. Those familiar with lung ultrasound will recall ‘A-lines”, which are reverberation artifacts that occur with the distinct interface between soft tissue and air. This artifact appears as bright hyperechoic equidistant horizontal lines [Fig. 3, Fig. 4]. In addition to placing the patient in the left lateral decubitus position, a ‘Scissors Maneuver’ has been described as a way to increase the diagnostic accuracy of pneumoperitoneum with ultrasound.4 It is performed by applying alternating pressure and gentle release (while still maintaining contact with the skin surface) on the abdominal wall with the linear probe. Firm pressure of the ultrasound probe displaces the free air resulting in a lack of reverberation artifacts, while gentle release of the probe reveals the presence of reverberation artifacts from free air.4
Enhancement of the Peritoneal Stripe Sign (EPSS)
The ‘Enhancement of the Peritoneal Stripe Sign’ (EPSS)* is a reliable and accurate sonographic finding in the diagnosis of pneumoperitoneum. The presence of tiny bubbles of free air in addition to the acoustic mismatch at the interface between soft tissue and air produces a bright hyperechoic peritoneal stripe [Fig. 3, Fig. 4].5,6 The enhancement of the peritoneal stripe sign has been found to have a sensitivity of 100% and specificity of 99% for the diagnosis of pneumoperitoneum 5.
*Not to be confused with the E-Point Septal Separation, used to estimate cardiac ejection fraction as described in a previous #US4TW case.
The major pitfall when looking for pneumoperitoneum with ultrasound is misinterpreting intraluminal air (i.e. normal air within the bowel) as extraluminal air (i.e. abnormal air outside of the bowel). One way to avoid this is to scan your patient at the right upper quadrant, where there is an absence of bowel. Use of the ‘shifting phenomenon’ described previously may also aid in avoiding this pitfall.
Disposition and Case Conclusion
After aggressive fluid resuscitation and intravenous antibiotics, the patient was stable for computed tomography (CT) of the abdomen, pending surgical consultation. The CT revealed:
“A moderate amount of free intraperitoneal air and fluid in keeping with hollow viscus perforation. There is a linear air track traversing the anterior wall of the gastric antrum, likely indicative of a perforated gastric ulcer.”
The patient was taken to the operating room emergently, where a perforated gastric ulcer was confirmed and repaired. After a prolonged stay in the intensive care unit, the patient has since been discharged in stable condition and is doing well.
Perforated viscus is a life-threatening cause of abdominal pain that requires prompt diagnosis and surgical consultation. Pneumoperitoneum is a true surgical emergency which requires surgical intervention in up to 90% of patients.6 While blunt trauma comprises about 3-15% of cases of hollow viscus injuries, it is missed in 20-50% of cases.7 While CT is considered the gold standard for diagnosis of perforated viscus, patients are often too acutely ill and unstable for CT. Upright and/or left lateral decubitus plain radiographs has been the traditional initial imaging modality of choice, however patient compliance can make the study difficult to obtain. Additionally, x-rays have been shown to reveal free air under the diaphragm in only 40-50% of patients with a confirmed hollow viscus injury.2,7
Point-of-care ultrasound is a tool that is widely used by emergency physicians to aid in elucidating a diagnosis in patients presenting with undifferentiated abdominal pain. Ultrasound has been shown to be a highly effective imaging modality to diagnose pneumoperitoneum with a higher sensitivity compared to x-ray [Table 1].
|Positive Predictive Value
Table 1. Comparison of test characteristics between ultrasound and plain radiography in the diagnosis of pneumoperitoneum.8
In fact, as little as 1 mL of free air can be identified with ultrasound.7 Thus, while the diagnosis of pneumoperitoneum is not a ‘core’ utilization of ultrasound for emergency physicians, it is important for us to be familiar with the classic findings as described above. Integrating the findings of pneumoperitoneum in a point-of-care ultrasound study can expedite patient care and surgical consultation, thus improving time to operative management and potentially improving patient outcomes.
Take Home Points
- Perforated viscus is a life-threatening cause of abdominal pain requiring prompt diagnosis and surgical consultation.
- Point-of-care ultrasound provides a higher sensitivity and diagnostic accuracy in diagnosing pneumoperitoneum compared to plain radiography8 with the added benefits of being able to be performed more rapidly and with better patient compliance.
- The key sonographic signs of pneumoperitoneum include:
- Enhancement of the peritoneal stripe sign
- Reverberation artifacts
- Shifting phenomenon
- Beware of the pitfall of mistaking intraluminal air for extraluminal air.