shades of grey…

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.

[wpvideo RPTvFF6u]   [wpvideo Y6Ff9ZfH]

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”
    • Gallbladder
    • Colon
    • Blood vessels
    • Fluid in stomach or bowel
  • Pre-menopausal women
    • will have physiologic pelvic fluid.
  • Non-traumatic pathology
    • Ascites
    • Renal failure with peritoneal dialysis
    • Ovarian cysts (especially with rupture)
    • Pelvic inflammatory disease
    • Pleural effusions
  • Traumatic pathology
    • Superficial liver or kidney lacerations
    • Haemothorax
    • Pelvic haematomas from pelvic #’s

Hope you find this helpful next time you slap on the probe….


  1. 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.
  2. Goodwin H, Holmes JF, Wisner DH. Abdominal ultrasound examination in pregnant blunt trauma patients. J Trauma. 2001 Apr;50(4):689-93
  3. Udobi KF et al. Role of ultrasonography in penetrating abdominal trauma: a prospective clinical study. J Trauma. 2001 Mar;50(3):475-9.
  4. 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.
  5. 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.
  6. American College of Emergency Physicians. Policy statement. Emergency ultrasound imaging criteria compendium. p 26. @ www.acep.org/workarea/downloadasset.aspx?id=32886

The Web.


Youtube “the Double-Line Sign”

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