What does an ultrasound showing no vascular (blood vessel) activity indicate?

From the Guidelines

Ultrasound without vascular imaging is not recommended as the primary diagnostic tool for patients with suspected pulmonary embolism (PE) or deep vein thrombosis (DVT), as it may not provide sufficient information to rule out these conditions. Instead, venous ultrasound is the preferred imaging method for the initial diagnosis of DVT, as it has been shown to detect asymptomatic DVT of the lower extremities in a significant proportion of patients with advanced cancer 1. When a decision is made to perform venous ultrasound as the initial imaging modality, a positive finding in a patient with symptoms consistent with PE can be considered evidence for diagnosis of VTE disease and may preclude the need for additional diagnostic imaging in the ED 1. However, if the ultrasound results are negative or indeterminate, other venous imaging modalities such as contrast-enhanced CT venography (CTV) or magnetic resonance venogram (MRV) with contrast may be recommended 1. It is essential to note that the diagnostic efficacy of ultrasound depends on whether it is performed before or after other diagnostic tests, and its specificity remains high (97%) in patients with PE 1. In summary, while ultrasound without vascular imaging may not be the primary diagnostic tool for PE or DVT, venous ultrasound is a valuable diagnostic method for detecting DVT, and its results should be interpreted in the context of the patient's clinical presentation and other diagnostic findings. Key points to consider when using ultrasound for diagnosing DVT or PE include:

• Venous ultrasound is the preferred imaging method for the initial diagnosis of DVT
• A positive finding on venous ultrasound can be considered evidence for diagnosis of VTE disease
• Other venous imaging modalities may be recommended if ultrasound results are negative or indeterminate
• The diagnostic efficacy of ultrasound depends on the context in which it is performed
• Ultrasound without vascular imaging may not provide sufficient information to rule out PE or DVT.

From the Research

Ultrasound Findings

• The use of ultrasound in diagnosing vascular issues has been studied extensively, with a focus on deep venous thrombosis (DVT) and peripheral vascular disease (PVD) 2, 3, 4, 5, 6.
• A study published in 1999 found that venous thrombosis was present in 27 of 136 patients with PVD, and that decreasing ankle-brachial pressure index (ABPI) was independently associated with an increased risk of DVT 2.
• Another study published in 2017 found that a complete duplex examination of the lower extremities can detect a range of conditions, including acute and chronic DVT, superficial venous thrombosis, and venous insufficiency, which may not be detected by a limited femoropopliteal (FP) ultrasound examination 3.

Non-Vascular Findings

• Ultrasound examinations can also detect non-vascular findings, such as masses (cysts, hematomas, solid masses, or aneurysms) 3, 4.
• A study published in 2009 found that 12% of ultrasound examinations for suspected DVT detected incidental findings, including pseudoaneurysm, arterial occlusive disease, vascular graft complication, compartment syndrome, and tumor 4.
• These findings highlight the importance of considering non-vascular causes of leg pain and swelling, and the potential benefits of a complete ultrasound examination 3, 4.

Diagnostic Approach

• The diagnosis of DVT requires a multifaceted approach, including clinical assessment, evaluation of pre-test probability, and objective diagnostic testing 5.
• The use of clinical decision rules, such as the Wells score, can help stratify patients into "unlikely" or "likely" categories for DVT, and guide further testing 5.
• Compression ultrasound is a commonly used diagnostic test for DVT, and can be used in conjunction with D-dimer testing to exclude DVT in patients with a low pre-test probability 5.