Postoperative evaluation of microvascularization in mandibular reconstructions with microvascular flaps – First results with a new perfusion software for contrast-enhanced sonography (CEUS)

Abstract

Quantitative measurement of dynamic contrast values obtained by contrast-enhanced ultrasound (CEUS) for evaluating microvascularization in osseous and osseocutaneous free flaps used for maxillofacial reconstructions. 22 patients (6 women, 16 men, mean age: 57 years, range: 47 to 82 years) who had received mandibular reconstructions with 3 avascular and 19 microvascular free osseous or osseocutaneous transplants were included in this trial. 16 patients had received a microvascular osseocutaneous fibular flap, 2 patients a microvascular osseous fibular flap and 1 patient a microvascular osseous iliac crest flap. Patients were followed up for 12 months on average (range: 3 to 20 months). Ultrasound examination was carried out by one experienced examiner with a linear probe (6-9 MHz, LOGIQ E9, GE) after the intravenous bolus injection of 2.4 ml contrast agent (SonoVue®, BRACCO, Germany). Digital cine loops were analysed with a quantification software (VueBox™) for determining wash-in parameters: Rise Time (RT), Peak Enhancement (PE), Wash-in Area Under the Curve (WiAUC) and Wash-in Rate (WiR). Results were compared with the patients' postoperative clinical outcome. For the bone area the median of the RT was 10.0 s (range 3.1 to 65.0 s), for the ratio between bone tissue and soft tissue for the PE the median was 10.4% (range 2.6 to 29.8%), the median for the WiAUC was 11.1% (range 1.5 to 77.7%) and the median for the WiR was 5.7 %(range 0.7 to 61.1%). None of the patients with microvascular osseocutaneous and osseous flaps showed any signs of transplant bone loss, which corresponded with the qualitative CEUS assessment. The patients with microvascular re-anastomosed transplants showed widely varying values for the investigated parameters (RT, PE, WiAUC, WiR). For patients with avascular bone transplants, these parameters were reduced to zero values for the bone area resulting in a significant difference (p < 0.05) for the PE compared to the patients with microvascular bone transplants. CEUS allowed the qualitative assessment of bone microvascularization by observing the transition of the contrast agent from the periostal area into the bone. However, defining a critical lower border by quantification of bone perfusion was difficult because of the inconstant perfusion of the bone transplants used in the trial.