Chyluria: non-enhanced MR lymphography.

Chyluria is an uncommon medical condition resulting from an abnormal communication between the abdominal lymphatic system and the urinary tract, which results in the presence of chyle in the urine, making it appear milky white. Proper diagnosis is demonstrated by the concentration of urinary lipids. Worldwide, chyluria is most commonly associated with the parasite Wuchereria bancrofti. However, in Europe and North America, where the condition is rare, non-parasitic etiologies predominate. Identifying the cause and location of the uro-lymphatic communication is essential in guiding therapeutic management, but imaging the lymphatic channels remains a challenge. Magnetic resonance (MR) lymphography, a non-invasive free-breathing 3D high-resolution fast-recovery fast spin-echo sequence similar to that used for 3D MR cholangiopancreatography, may demonstrate the cause and location of an abnormal communication between the lymphatic system and urinary tract. In parasitic causes of chyluria, dilated lymphatics vessels communicating with the lymphatic system are demonstrated. In non-parasitic causes of chyluria channel type lymphatic malformations are the most common. Markedly dilated and dysplastic lymphatic vessels communicating with the urinary tract are demonstrated. In addition, other cystic or channel type lymphatic malformations such as thoracic, soft tissue or bone abnormalities may be observed. This review describes the abdominal lymphatic diseases leading to chyluria and presents the technique and images obtained with non-enhanced MR lymphography to enable radiologists in identifying and classifying uro-lymphatic fistulae.Critical relevance statement: Non-enhanced MR lymphography enables the identification and categorization of uro-lymphatic fistulae.

Global versus individual muscle segmentation to assess quantitative MRI-based fat fraction changes in neuromuscular diseases.

OBJECTIVES: Magnetic resonance imaging (MRI) constitutes a powerful outcome measure in neuromuscular disorders, yet there is a broad diversity of approaches in data acquisition and analysis. Since each neuromuscular disease presents a specific pattern of muscle involvement, the recommended analysis is assumed to be the muscle-by-muscle approach. We, therefore, performed a comparative analysis of different segmentation approaches, including global muscle segmentation, to determine the best strategy for evaluating disease progression. METHODS: In 102 patients (21 immune-mediated necrotizing myopathy/IMNM, 21 inclusion body myositis/IBM, 10 GNE myopathy/GNEM, 19 Duchenne muscular dystrophy/DMD, 12 dysferlinopathy/DYSF, 7 limb-girdle muscular dystrophy/LGMD2I, 7 Pompe disease, 5 spinal muscular atrophy/SMA), two MRI scans were obtained at a 1-year interval in thighs and lower legs. Regions of interest (ROIs) were drawn in individual muscles, muscle groups, and the global muscle segment. Standardized response means (SRMs) were determined to assess sensitivity to change in fat fraction (ΔFat%) in individual muscles, muscle groups, weighted combinations of muscles and muscle groups, and in the global muscle segment. RESULTS: Global muscle segmentation gave high SRMs for ΔFat% in thigh and lower leg for IMNM, DYSF, LGMD2I, DMD, SMA, and Pompe disease, and only in lower leg for GNEM and thigh for IBM. CONCLUSIONS: Global muscle segment Fat% showed to be sensitive to change in most investigated neuromuscular disorders. As compared to individual muscle drawing, it is a faster and an easier approach to assess disease progression. The use of individual muscle ROIs, however, is still of interest for exploring selective muscle involvement. KEY POINTS: • MRI-based evaluation of fatty replacement in muscles is used as an outcome measure in the assessment of 1-year disease progression in 8 different neuromuscular diseases. • Different segmentation approaches, including global muscle segmentation, were evaluated for determining 1-year fat fraction changes in lower limb skeletal muscles. • Global muscle segment fat fraction has shown to be sensitive to change in lower leg and thigh in most of the investigated neuromuscular diseases.

Severe axial and pelvifemoral muscle damage in immune-mediated necrotizing myopathy evaluated by whole-body MRI.

BACKGROUND: Our objective was to define the pattern and severity of muscle damage in immune-mediated necrotizing myopathy (IMNM) and its relationship with clinical and serological features. METHODS: IMNM patients with a whole-body MRI (n=42) were included and compared to sporadic inclusion-body myositis (s-IBM) patients (n=60). Fat replacement was estimated using the Mercuri score in 55 muscles. Overall lesion load was defined as the sum of all abnormal Mercuri scores (reported in % maximal score) and lesion load quotient was defined as the overall lesion load divided by disease duration. Linear relationships between variables were assessed and multidimensional analysis was performed to define homogenous groups of patients. RESULTS: IMNM patients were aged 48.1±15.8 years and had a disease duration of 9.8±8.1 years. Most severely affected muscle groups were located in the pelvifemoral and lumbar region. Unsupervised analysis showed two subgroups of patients: one with mild lesion load (15±10%, n=32/42) and another with severe lesion load (60±10%, n=10/42: p<0.001) associated with a mean disease duration of 6.8±6.0 years and 19.5±5.7 years, respectively (p<0.0001). Correlational studies confirmed that disease duration was the most important predictor of muscle damage. Multivariate analyses demonstrated a more severe involvement in select muscle groups in females and seropositive patients. No difference was found in overall lesion load quotient of IMNM compared to IBM (p=0.07) but with a distinct muscle pattern. CONCLUSION: IMNM is associated with severe axial and pelvifemoral muscle damage. Disease duration is an important predictor of muscle damage. IMNM and s-IBM patients have a comparable damage burden.