Ultrasound Shear-Wave Elastography for Follow-Up Fat Induration after Breast Reconstruction with an Autologous Flap.

Fat induration is associated with necrosis and remains a common complication in breast reconstructions with autologous flaps after mastectomy. Fat induration can cause deep tissue infection, pain, distress, and anxiety. However, the diagnosis for this problem has not been objectively defined. In the current article, We will share our experience of using ultrasound shear-wave elastography with 14 patients who had clinical fat induration after breast reconstruction with a deep inferior epigastric perforator (DIEP) flap. The experience suggested that shear wave elastography may be a noninvasive tool to assess alterations of tissue stiffness in a reproducible fashion after breast reconstruction with DIEP flaps. Complications, such as fat necrosis and fatty induration, may occur as a result of unstable blood flow to the flap. Thereby, objective assessments of stiffness might make a major contribution to the understanding of hemodynamics of the DIEP flap after transplantation.

Fatty induration that is associated with necrosis remains a common complication in breast reconstructions with autologous flaps after mastectomy.[1,2] Fat induration can cause deep tissue infection, pain, distress, and anxiety. However, the diagnosis for this problem has not been objectively defined. Clinically, palpation has always been an important approach in detecting fat induration; but this approach is subjective and lacks sensitivity for small or deeply located lesions. A hardness meter, such as a durometer, can be useful, but provides only one-dimensional data.

Ultrasound elastography, especially shear-wave elastography (SWE), is a relatively new technology that entered the clinic in the last decade. SWE is an imaging technique that quantifies tissue stiffness by measuring the speed of shear waves in the tissue.[3] The speed can either be directly used as an indicator of stiffness or converted to Young’s modulus. A low speed corresponds to a soft tissue, whereas a high speed indicates a stiff tissue. This system displays real-time, color-coded elastograms of either the shear wave speed (m/sec) or elastic modulus (kPa) in a one-dimensional map, and quantitative measurements can be obtained within a region of interest (Fig.1). Since its introduction, ultrasound elastography has enabled the evaluation of many different types of organs, including the breast, liver, prostate, thyroid glands, blood vessels, salivary glands, musculoskeletal structures, and cervical lymph nodes.[4]

Fig. 1.

Shear-wave elastographic color images. The ranges of maximum elasticity value are shown using a default color scale that ranges from 0 to +180 kPa. The maximum elasticity colors on SWE can be classified into 3 categories: dark blue and light blue indicating soft elasticity, green and orange indicating intermediate elasticity, and red indicating hard elasticity.

The device used in this study was a GE Healthcare LOGIQ E9 ultrasound scanner with real-time SWE and a 9L linear (4–9 MHz) probe (GE Healthcare, Amersham Place, Little Chalfout, Buckinghamshire, UK). This device can quantify tissue stiffness by measuring the speed of shear waves in tissues and can display the data on an absolute scale. Our experience with 14 fat induration cases suggested that SWE may be a noninvasive tool to assess alterations of tissue stiffness in a reproducible fashion after breast reconstruction with DIEP flaps. Our preliminary data indicated that fatty induration was often localized in the distal region in Hartrampf zone II (8 cases, 57.1%), which is consistent with the previous angiosome concept in the DIEP flap method (Fig. 2).[4] Degree of stiffness measured by SWE had a consistent correlation with that by palpation.

Fig. 2.

Correlation between location of fat induration and 2 different clinical diagnoses. SSM indicates skin-sparing mastectomy; TM, total mastectomy; IId, distal part of ZONE II; IIp, proximal part of ZONE II; IIm, middle part of ZONE II; IIId, distal part of ZONE III +, mild; ++, not great; +++, great.

Following are 2 representative cases. A 53-year-old patient (case no 7), who underwent left breast reconstruction with an adipose DIEP flap based on a single, large, and contralateral medial row perforating vessel, had a sustained fatty induration for 6 months (Fig. 3A) in the superior medial area of the breast. SWE was used to investigate fatty stiffness quantitatively and showed increased stiffness (mean, 22.3 kPa) when compared with lateral area (mean, 6.6 kPa) (Fig. 3B). A 62-year-old patient (case no 8), who underwent left breast reconstruction with a cutaneous-adipose DIEP flap based on a single, small, and contralateral medial row perforating vessel 10 months ago, complained of breast mass with pain and stiffness in the medial region (Fig. 4A). B-mode imaging showed that the breast mass was likely not postoperative edema or hematoma. SWE showed a significantly higher stiffness (mean, 107.4 kPa) when compared with the lateral area (mean, 13.9 kPa) (Fig 4B). These findings indicated that the breast mass was associated with fat necrosis.

Fig. 3.

A, 6 months status post left deep inferior epigastric perforator flap with complaint of palpable hard region in upper medial breast, frontal view. B, SWE showed a significantly higher stiffness toward the upper medial region although that was not recognized by appearance.

Fig. 4.

A, 10 months status post left deep inferior epigastric perforator flap with suspicion of fat necrosis in superior medial breast, frontal view. B, SWE showed a significantly higher stiffness toward the upper medial region.

Ultrasound elastography techniques can be broadly divided into 2 groups: strain elastography and shear wave-based elastography. We strongly recommend this technique in combination with either B-mode image or SWE for detection of tissue deformation or stiffness. The strain ratio was calculated by dividing the mean strain of the reference normal tissue by the mean strain within the breast lesion. However, there is no consistency in selecting the reference normal tissue. Unlike strain elastography, SWE quantifies tissue stiffness on an absolute scale. Fat induration or necrosis is a well-recognized complication after autologous reconstruction that can give an unfavorable result. Care should be taken to thoroughly evaluate these firm areas, and if any concern exists regarding the diagnosis, SWE is recommended to successfully detect suspected areas of fatty induration while maintaining a favorable breast contour. The early recognition and precise diagnosis of fatty induration by SWE might enable good management, unlike surgical excision or liposuction accompanied with contour deformities. For instance, a simplified technique called “needle aeration” is effective for managing early recognized hard nodules of fat necrosis in a population of patients who had undergone previous autologous breast reconstruction.[5]

Stiffness of adipose tissue after breast reconstruction with autologous flaps is considered to be strongly associated with the hemodynamics of the DIEP flap. Complications, such as fat induratin or necrosis, may occur as a result of unstable blood flow to the flap.[6,7] Thereby, objective assessments of stiffness might make a major contribution to the understanding of hemodynamics of the DIEP flap after transplantation.

CONCLUSIONS

Our preliminary experience suggests that SWE may be useful in facilitating surgical follow-up and acceptable in clinical practice. Although ultrasonography is a technique that can be widely used in daily practice and has defined the size and location of tissue deformations, there are no reports that measure stiffness using ultrasound elastography. For the future, the optimal cut-off values for either significant fat induration or necrosis after breast reconstruction using the autologous flap procedure should be determined to define the diagnostic criteria and provide further reliability.

ACKNOWLEDGMENTS

All experimental procedures and protocols for animals conformed to the National Institutes of Health Guide for the Care and Use of Laboratory Animals and were approved by the Committee for Animal Research of Kyoto Prefectural University of Medicine.