Comparing Ultrasonography With Magnetic Resonance Imaging in the Detection of Deep Tissue Injury

© 2024 HMP Global. All Rights Reserved.

Any views and opinions expressed are those of the author(s) and/or participants and do not necessarily reflect the views, policy, or position of Wounds or HMP Global, their employees, and affiliates.

DTI, which was defined by the National Pressure Ulcer Advisory Panel in the United States in 2005 as a pressure-related injury to the subcutaneous tissue under intact skin, has been the focus of several studies since then.¹ Patients with spinal cord injuries are at high risk of DTI because of being seated in a wheelchair for long periods of time during daily life and because of sensory impairments.² DTI develops from within deep tissues such as fat and muscle and progresses to the skin surface, and it is often detected after purple or maroon localized areas are observed on the skin.³ DTI is difficult to detect, and by the time the injury becomes visible, extensive injury to the underlying tissue has often already occurred.⁴ These injuries can progress rapidly to severe and difficult-to-heal stage 3 or stage 4 pressure ulcers.^5,6 In more severe cases, these injuries can lead to potentially life-threatening infection and sepsis.⁷ Meanwhile, in some cases DTIs are detected before they reach the skin surface^8,9; the authors of the current case report call such instances early detection. Thus, it is essential to detect DTI early and to provide preventive intervention before it progresses to a deep pressure ulcer.⁸

Previous attempts to detect subcutaneous injuries using ultrasonography,^3,8-11 computed tomography,¹² and MRI^4,13 have been reported. Current guidelines provide no definitive description of imaging studies in the diagnosis of deep lesions, although a small number of case reports suggest that ultrasonography may be predictive¹⁰ and that MRI has enabled early visualization of deep lesions.¹³ However, there are few reports comparing ultrasonography and MRI for the detection of DTI. 

This report presents 2 cases of DTI that were detected early using imaging studies and compares ultrasonography with MRI for the detection of DTI specifically. This study was approved by the research ethics committee of Wakayama Medical University (approval No. 3303), and informed written consent was obtained from the 2 patients in the study.

Case 1

Case 1 is a 28-year-old male with incomplete paraplegia (American Spinal Injury Association Impairment Scale type B injury) at the C5 level resulting from a fall 3 years previously. He had undergone debridement and reconstructive surgery with a V-Y advancement flap at a previous hospital for osteomyelitis and deep pressure ulcer in the sacral region. He was transferred to Kibikogen Rehabilitation Center for Employment Injuries for postoperative rehabilitation. On physical examination at admission, no skin abnormalities were observed on the patient’s buttocks. However, MRI performed for postoperative follow-up of sacral osteomyelitis after admission showed areas of high signal intensity in the subcutaneous soft tissue below both ischia on T2-weighted fat-suppressed images, which were suspicious for DTI (Figure 1A, 1B). Ultrasonography confirmed findings suggestive of DTI, including an unclear layered structure, hypoechoic lesions, and superficial and deep fascial discontinuities (Figure 1C, 1D).

The patient had been in a wheelchair 12 hours a day for the past year and had difficulty pushing up from the chair for decompression. As part of the intervention, interface pressure was measured by the pressure mapping systems (range, 0 mm Hg–350 mm Hg). The values were as high as 319 gf/cm² at the left ischial region and 325 gf/cm² at the right ischial region with the patient using an air cell-based high-profile cushion while seated in a wheelchair (Figure 2A). The authors of the current report advised the patient on cushion selection and decompression movements. Based on the results of the interface pressure measurement, the patient was instructed to achieve decompression by leaning forward for a period of several seconds every 15 minutes (Figure 2B). The detection of DTI by MRI may have led to early intervention and healing in this patient, who was discharged 3 months later without progression to a deep pressure ulcer.

Case 2

A 65-year-old male with complete paraplegia (American Spinal Injury Association Impairment Scale type A injury) at the T1 level resulting from a fall 9 years previously was admitted to Kibikogen Rehabilitation Center for Employment Injuries for a lower gastrointestinal endoscopy as a routine medical checkup. Physical examination on admission revealed no skin abnormalities on either buttock. The patient had been in a wheelchair 15 hours a day for the past year and, because of his obesity, had difficulty pushing himself up from the chair for decompression. The interface pressure measurements were 264 gf/cm² for the left ischial region and 179 gf/cm² for the right ischial region with the patient using an air cell-based high-profile cushion while seated in his wheelchair. The left ischial region had higher pressure and thus, was considered to be at higher risk of DTI. Because of the patient’s obesity and the thick subcutaneous soft tissue, and the perceived difficulty of screening for DTI by assessing deep tissue by ultrasonography only, MRI was also performed. Ultrasonography showed no abnormal findings (Figure 3A). However, T2-weighted fat-suppressed MRI showed a significant area of high signal intensity in the subcutaneous soft tissue of the left buttock, which was suspicious for DTI (Figure 3B). 

After 3 months of careful follow-up, no abnormalities were apparent based on external appearance of the skin; however, ultrasonography showed findings suggestive of DTI in the left ischial region, including unclear layered structures, hypoechoic lesions, and superficial fascial discontinuities (Figure 3C). After a further 3 months of cushion adjustment and teaching the patient aggressive decompression and transferring movements, resolution of DTI was observed on both ultrasonography and MRI (Figure 3D, 3E).

The clinical signs of DTI include skin changes on visual inspection, such as a purple or reddish-brown localized area of discolored intact skin or a blood-filled blister, and/or induration on palpation as a result of deep soft tissue injury.⁹ Muscle tissue is more susceptible to pressure ischemia than is the skin.⁸ This tissue injury occurring at depth under normal skin can be detected by imaging before such injury becomes clinically apparent.^8,9 The clinical prognosis of DTI varies from cases that can heal without skin defects to cases that result in deep pressure ulcers.^10,14-16 The authors of the current report believe that DTI may be reversible if it is detected early, as in case 2. However, the development of deep pressure ulcers not only affects the patient’s quality of life but also places a significant burden on the health care system, both financially and on the health care providers who treat affected patients.¹¹ Thus, it is essential to detect subcutaneous abnormality at an early stage to initiate early intervention and achieve healing. 

Several imaging modalities, including ultrasonography and MRI, have the potential for confirming the findings of DTI.^3,8-11,13 Some reports indicate that subcutaneous abnormalities have been identified by ultrasonography,^8-10 but few reports have discussed such identification using MRI.¹³ The current case report discusses 2 cases of early detection of DTI by ultrasonography and MRI, and compares these imaging modalities. Ultrasonography is most frequently used due to its noninvasive nature and low cost, and because it can be quickly used at the bedside for evaluation.^3,17-19 Drawbacks of ultrasonography include poor reproducibility and individual differences between examiners, difficulty detecting whether the subcutaneous tissue (including adipose and muscle tissue) in the DTI region has actually been injured,²⁰ and lack of specificity regarding tissue injury localization.²¹ MRI has been said to be markedly superior to ultrasonography because it can provide more precise localization and extension of ischemic injuries in muscle and soft tissue, and it can detect bone lesions, such as osteomyelitis and heterotopic bone formation.²² It has also been suggested that the response to injury starts at some distance from the point of deformation, highlighting the importance of evaluating the mechanical response in 3 dimensions with MRI.²³ However, MRI has important drawbacks, including long acquisition time, high inspection cost, and the confined environment.²⁴

The characteristic ultrasonographic findings of DTI consist of an unclear layered structure, a hypoechoic lesion, discontinuous superficial or deep fascia, and a heterogeneous hypoechoic area.¹⁰ In particular, the presence of discontinuous deep fascia or heterogeneous hypoechoic areas are particularly concerning for DTI.¹⁰ In the current case report, although there was no abnormality on the skin surface in either case 1 or case 2, both patients had ultrasonographic characteristics of DTI as well as discontinuous fascia, and the authors of the current report were concerned that DTI could worsen in the future. In contrast, findings suggestive of DTI were observed on T2-weighted fat-suppressed MRIs, which clearly showed regions of high signal intensity in the subcutaneous soft tissues below the bone. In case 1, MRI findings showed abnormal shadows from both ischial tuberosities to the subcutaneous tissue, confirming the bottom-up theory of the progression of DTI development from the deep layers to the superficial skin as discussed in Ankrom et al.²⁵ In case 2, MRI showed extensive abnormal shadows in the subcutaneous soft tissue of the left buttock. This finding is similar to that of a previously reported case of DTI in the thigh that was confirmed by MRI.¹³

Further supporting the use of MRI, in case 2, abnormal findings were detected by MRI 3 months before features of DTI were identified by ultrasonography. Although obesity and thick subcutaneous soft tissue may have made it difficult to detect DTI on ultrasonography in this patient, abnormal findings were clearly identified on MRI, suggesting that deeper tissue can be visualized earlier by MRI than by ultrasonography. Consequently, the authors of the current report propose that MRI may be superior to ultrasonography for detecting DTI and that use of MRI would lead to earlier intervention and healing. In practice, MRI is sometimes disregarded because of the high cost (approximately $350 as of 2019 in the United States according to Medicare reimbursement data, depending on the facility) and lengthy examination time.²⁶ However, in terms of the economic burden of DTI, 11% to 26% of DTI cases reportedly progress to deep pressure ulcers,^27,28 and a 2007 publication reported that DTI costs up to $70 000 per case for surgical and medical treatment when it progresses to full-thickness pressure ulcers.²⁹ Thus, the authors of the current report propose that MRI could be a screening tool for patients with spinal cord injury who are at high risk for DTI, with the understanding that MRI may not be appropriate for every patient.

The current case report has limitations, including its small size, with only 2 cases. Further studies involving a larger number of patients are needed to establish a standard protocol, including the most applicable cases for MRI screening and the optimal period in which scans should be performed for screening and follow-up.

The 2 cases in this report suggest that detection of DTI by MRI may lead to earlier preventive intervention and treatment of pressure ulcers. The authors of the current report plan to conduct studies in support of assessing the use of MRI as a screening tool for individuals with spinal cord injury who are at high risk of DTI. Specifically, the authors are conducting an observational study using MRI screening for 50 patients with spinal cord injury, comparing the primary outcome (eg, body mass index, interface pressure, wheelchair time, frequency of decompression procedures) of the DTI-positive and DTI-negative groups to identify risk factors for DTI. 

Authors: Yasuhiro Sakata, MD^1,2; Takanori Namba, MD, PhD³; Yasunori Umemoto, MD, PhD⁴; Tatsuya Yoshikawa, MD, PhD⁵; Kazunari Furusawa, MD, PhD³; and Shinichi Asamura, MD, PhD²

Affiliations: ¹Department of Plastic and Reconstructive Surgery, Kishiwada Tokushukai Hospital, Kishiwada, Japan; ²Department of Plastic Surgery, Wakayama Medical University, Wakayama, Japan; ³Department of Rehabilitation Medicine, Kibikogen Rehabilitation Center for Employment Injuries, Kibichuo, Japan; ⁴Department of Rehabilitation Medicine, Yokohama City University, Yokohama, Japan; ⁵Department of Rehabilitation Medicine, Sano Memorial Hospital, Osaka, Japan

Disclosure: The authors disclose no financial or other conflicts of interest.

Ethical Approval: Both patients presented in this article provided written informed consent.

Correspondence: Yasuhiro Sakata, MD; Department of Plastic and Reconstructive Surgery, Kishiwada Tokushukai Hospital, 4-27-1 Kamori-cho, Kishiwada, Osaka, 596-8522, Japan; ysakata@wakayama-med.ac.jp

Manuscript Accepted: August 20, 2024