What is the magnetic resonance imaging (MRI) workup for red marrow related changes in the pelvic bone?

From the Guidelines

MRI is the preferred imaging modality for evaluating red marrow changes in the pelvic bones, and a standard protocol should include T1-weighted, T2-weighted, and STIR sequences, with the addition of contrast-enhanced T1-weighted images when necessary, as recommended by recent studies 1. When assessing red marrow changes, it's essential to distinguish between benign and pathological conditions. Normal red marrow appears hypointense on T1-weighted images and slightly hyperintense on T2-weighted and STIR sequences.

• Key characteristics of benign red marrow reconversion include homogeneous signal intensity, following the normal distribution pattern of red marrow, and lacking focal lesions.
• Pathological conditions, such as metastases, primary bone tumors, or infiltrative bone marrow disorders, often exhibit heterogeneous signal intensity, irregular distribution, and focal lesions. Diffusion-weighted imaging (DWI) can be particularly helpful in evaluating red marrow changes, as restricted diffusion often indicates malignancy 1.
• The use of DWI has been shown to increase the diagnostic performance of MRI studies and reduce the need for contrast medium administration.
• Single-shot echo planar imaging (SSH-EPI) sequences are recommended, with the acquisition of at least two b values being necessary to allow the calculation of ADC. For indeterminate findings, follow-up imaging in 3-6 months may be necessary to assess for stability or progression.
• In cases where malignancy is suspected, additional imaging such as whole-body MRI, PET/CT, or targeted biopsies may be warranted. The radiologist should correlate findings with the patient's clinical history, including age, underlying conditions, medication use (particularly growth factors or chemotherapy), and previous imaging studies to accurately interpret red marrow changes in the pelvis 1.
• It's crucial to consider the patient's clinical context and medical history when interpreting imaging findings to avoid misdiagnosis or misinterpretation.

From the Research

MRI Evaluation of Red Marrow Changes in Pelvic Bone

• The appearance of hematopoietic marrow in magnetic resonance (MR) imaging is variable, and differences between normal and pathologic marrow may be subtle 2.
• A consistent pattern of morphologic change was noted as hematopoietic marrow converted to fatty marrow with increasing age, with hematopoietic marrow becoming more focal and sharply defined, usually in the form of islands of residual hematopoietic marrow 2.
• Periarticular hematopoietic marrow predominated in the sacroiliac region, with little residual hematopoietic marrow noted in the symphysis pubis and hip joints 2.
• Hematopoietic marrow persisted longer in juxtacortical locations, was always symmetric, remained less intense than fat on T2-weighted images, and usually had a central focus of fat 2.

Age-Related Marrow Changes

• Marrow signal intensity increased in all pelvic regions except the acetabulum from birth to age 24 years, with marrow heterogeneity being most prominent in the acetabulum at all ages 3.
• Patterns of bone marrow signal intensity and heterogeneity are recognized for four age groups: the infant, child, adolescent, and young adult, with regional and age-related differences in the signal intensity of pelvic marrow correlating with the percentage of fat seen microscopically in marrow 3.

Differentiation of Benign and Malignant Lesions

• Imaging parameters derived from T1-weighted imaging, diffusion-weighted imaging, and dynamic contrast-enhanced magnetic resonance imaging can be used to differentiate bone metastases from prostate cancer and benign red marrow depositions of the pelvic bone 4.
• The apparent diffusion coefficient, volume transfer constant, reflux rate, and volume fraction of the extravascular extracellular matrix values were significantly higher in bone metastases than in benign red marrow depositions, with area under the curves of 0.896,0.844,0.812, and 0.724, respectively 4.

Radiation-Induced Changes

• Fatty replacement of bone marrow was seen in all patients after pelvic radiation therapy, with pelvic bone complications and focal red marrow changes identified in 31.1% of patients 5.
• Pelvic insufficiency fracture, radiation osteitis, and avascular necrosis of the femoral head were diagnosed in 13.9%, 4.1%, and 0.8% of patients, respectively, with focal red bone marrow changes seen in 12.3% of patients 5.