Acoustic Radiation Force Impulse Elastography Assessment of Lymphoedema Tissue: An Insight into Tissue Stiffness

Abstract

Palpation remains essential for evaluating lymphoedema to detect subtle changes that may indicate progression. As palpation sense is not quantifiable, this study investigates the utility of ultrasound elastography to quantify stiffness of lymphoedema tissue and explore the influence of the pitting test on tissue stiffness. Fifteen women with unilateral arm lymphoedema were scanned using a Siemens S3000 Acuson ultrasound (Siemens, Germany) with 18 MHz and 9 MHz linear transducers to assess tissue structure and tissue stiffness with Acoustic Radiation Force Impulse elastography. Ninety sites were assessed, three on each of the lymphoedema-affected and contralateral unaffected arms. A subgroup of seven lymphoedema-affected sites included additional elastography imaging after a 60-s pitting test. Dermal tissue stiffness was greater than subcutaneous tissue stiffness regardless of the presence of pathology (p < 0.001). Lymphoedematous tissue exhibited a higher dermal to subcutaneous tissue stiffness ratio than contralateral sites (p = 0.005). Subgroup analysis indicated that the pitting test reduces dermal tissue stiffness (p = 0.018) and may alter the stiffness of the subcutaneous tissue layer. Elastography demonstrates potential as a complement to lymphoedema palpation assessment. The novel pre-test and post-pitting elastography imaging protocol yielded information representative of lymphoedema tissue characteristics that could not be ascertained from pre-test elastography images alone.

Keywords: ARFI; elastography; lymphoedema; pitting; pitting test; tissue stiffness; ultrasound.

Figure 1

Elastography maps indicative of tissue stiffness distribution observed between unaffected and lymphoedema-affected tissue (posterior forearm, participant 11). The unaffected tissue is relatively homogenous in colour across the dermal and subcutaneous layers, with a tissue stiffness ratio of 1.38 (left panel). There is a difference in tissue stiffness between tissue layers of the lymphoedema-affected site with a tissue stiffness ratio of 2.69 (right panel). The subgroup analysis of seven sites compared elastographic imaging before and after a 60-s pitting test. In Figure 2, pre-test images for each series are similar, with a heterogenous elastographic map showing lymphoedema-affected dermal stiffness greater than subcutaneous stiffness.

Figure 2

Pre-test and post-pitting test elastographic maps of lymphoedema-affected tissue. Lymphoedema-affected pre-test elastographic maps are heterogenic with high dermal stiffness (bright green) and relatively low subcutaneous stiffness (dark blue) (A1,B1,C1). Series A and B illustrate tissue stiffness reduction in both tissue layers post-pitting test. Stiffness is retained within the tissue layer where an intact border is apparent (A2), and the stiffness is altered within the test zone where there appears to be tissue border deterioration (B2). Tissue response was inconsistent among participants, with example (C2) showing a reduction in dermal stiffness and an increase in subcutaneous layer tissue stiffness post-pitting test, indicative of tissue compositional change.