Using four-point subcutaneous injection of lymphatic contrast-enhanced ultrasound to diagnose lymphedema of lower extremity.

Background: The diagnosis of lymphedema primarily relies on the clinical symptoms, signs, medical history and imaging. Objective lymphatic imaging helps improving the diagnosis of lymphedema. This study aimed to develop an effective imaging tool to diagnose lymphedema. Methods: This is a single-center retrospective study. From September 2022 to November 2023, we enrolled thirty-two patients, involving 40 lower extremities who underwent lymphatic contrast-enhanced ultrasound (CEUS) following a subcutaneous injection of contrast agent at four points in the First Affiliated Hospital of Sun Yat-sen University. Cohen's kappa value, sensitivity, specificity, positive predictive value, negative predictive value and accuracy were calculated. Lymphoscintigraphy was the reference standard. Results: Successful lymphatic-CEUS detection was defined as the situation that lymphatic drainage of medial or lateral lower limbs were observed. The successful detection rate was 100% (40 of 40). The diagnosis of lymphedema was based on the presence of either medial or lateral lymphatic obstructions, or subcutaneous lymphatic enhancement. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy for diagnosing lymphedema by lymphatic-CEUS were as follows: 91.2% (31 of 34), 100% (6 of 6), 100% (31 of 31), 66.7% (6 of 9) and 92.5% (37 of 40), respectively. The Cohen's Kappa value was 0.756. The area under the receiver operating characteristic curve (AUC) for the subcutaneous injection of four-point lymphatic-CEUS was 0.956. Conclusions: This study put forward a novel four-point lymphatic-CEUS method to detect the functions of the lymphatics of lower extremities and established a lymphatic-CEUS standard for diagnosing lymphedema of lower extremities. Four-point lymphatic-CEUS is a considerable option for diagnosing lymphedema of lower extremities.