A few days ago I was looking after a 31/40 gestation restrained passenger from low-speed MVA with a slight seatbelt abrasion in her RIF & mild suprapubic pain. She looked well, HR 70 with BP 108 systolic and no features of peritonism.
As I placed the US-probe on for her FAST, this was the first image I acquired…..
This immediately raised my anxiety and increased my sphincter tone…
…. however the remainder of her scan was ok, including a moving bub with a foetal heart rate of 136 bpm.
So I went back to the RUQ and was able to acquire the following….
The more I play with ultrasound the more I realise that it isn’t all just shades of grey. The application of colour-flow, colour-power or Doppler can assist by adding the extra dimension needed to the study to help you answer your clinical question.
In this case, I was looking at a ‘false positive’ which is likely a large blood vessel (venous).
The patient remained stable & was transferred to Maternity for CTG monitoring & a tertiary survey later in the evening…..
This case led to a brief literature search looking at incorrectly positive FAST scans & their true diagnoses. There is an abundance of literature regarding the False-negative FASTs with pearls and pitfalls in reducing our false-negative rates. Understandably, we do not want to miss the patient with intraabdominal fluid quietly bleeding away under our noses, however I feel it is also crucial to not over call the false positive studies as well (as this will lead to further unwarranted & potentially invasive investigation).
I’ve come up with the following list…
False Positive FAST Exam:
- Normal anatomical structures
- Perinephric fat
- the “Double-line sign”
- Blood vessels
- Fluid in stomach or bowel
- Perinephric fat
- Pre-menopausal women
- will have physiologic pelvic fluid.
- Non-traumatic pathology
- Renal failure with peritoneal dialysis
- Ovarian cysts (especially with rupture)
- Pelvic inflammatory disease
- Pleural effusions
- Traumatic pathology
- Superficial liver or kidney lacerations
- Pelvic haematomas from pelvic #’s
Hope you find this helpful next time you slap on the probe….
- Sierzenski PR et al. The double-line sign: a false positive finding on the Focused Assessment with Sonography for Trauma (FAST) examination. J Emerg Med. 2011 Feb;40(2):188-9. Epub 2009 Oct 2.
- Goodwin H, Holmes JF, Wisner DH. Abdominal ultrasound examination in pregnant blunt trauma patients. J Trauma. 2001 Apr;50(4):689-93
- Udobi KF et al. Role of ultrasonography in penetrating abdominal trauma: a prospective clinical study. J Trauma. 2001 Mar;50(3):475-9.
- Chi Leung Tsui et al. Focused abdominal sonography for trauma in the emergency department for blunt abdominal trauma. Int J Emerg Med. 2008 September; 1(3): 183–187.
- Lee BC et al. The utility of sonography for the triage of blunt abdominal trauma patients to exploratory laparotomy. AJR Am J Roentgenol. 2007 Feb;188(2):415-21.
- American College of Emergency Physicians. Policy statement. Emergency ultrasound imaging criteria compendium. p 26. @ www.acep.org/workarea/downloadasset.aspx?id=32886
Youtube “the Double-Line Sign”
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