Focused Ultrasound of the Popliteal Fossa for Detection of Symptomatic Baker's Cysts in Patients With Suspected Deep Vein Thrombosis: A Pilot Diagnostic Accuracy Study

Patients with suspected deep vein thrombosis (DVT) are commonly evaluated using clinical probability assessment, D-dimer testing, and compression ultrasonography. However, a substantial proportion of patients referred for DVT evaluation are ultimately diagnosed with alternative conditions that may explain their symptoms. One such condition is a symptomatic Baker's cyst, which may present with unilateral leg pain, swelling, or discomfort that clinically mimics DVT.

In current clinical practice, radiologist-performed complete compression ultrasound of the lower extremity (CCUS) is primarily used to confirm or exclude DVT. Although Baker's cysts are frequently identified during these examinations, their potential role as an early alternative diagnosis within the diagnostic pathway has not been systematically investigated. A focused ultrasound examination of the popliteal fossa (FUP) may allow emergency department (ED) or primary care clinicians to identify symptomatic Baker's cysts before referral for further DVT workup.

This prospective pilot study primarily aims to evaluate the feasibility of conducting a future definitive study investigating the role of FUP in patients with suspected DVT. Key feasibility outcomes include recruitment rates, scan completion rates, workflow integration, procedure timing, and practical implementation within routine emergency care. In addition, the study will generate preliminary diagnostic accuracy estimates regarding the ability of ED physicians and trained research assistants to identify symptomatic Baker's cysts using FUP, with CCUS serving as the reference standard. These data will be used to estimate outcome variance and inform sample size calculations and study design for a future definitive validation study.

This single-center pilot study will be conducted at Aarhus University Hospital, Denmark, among adult patients referred to the ED with suspected DVT. All participants will receive standard diagnostic evaluation and management according to current guidelines. The study-specific FUP examination will be performed before D-dimer and/or CCUS results are available, and FUP findings will not influence clinical decision-making during the study.

Inclusion criteria

• Age ≥ 18 years
• Clinical signs and symptoms of DVT, prompting the treating physician to initiate d-Dimer or CCUS diagnostic strategies

Exclusion criteria

• Prior inclusion
• FUP performed following d-Dimer or CCUS result already revealed