Bone marrow magnetic resonance imaging (MRI): morphological and functional features from reconversion to infiltration

Abstract

Bone marrow is a dynamic organ with variable composition in relation to age or pathophysiological changes. Magnetic resonance imaging (MRI) is the technique of choice to assess the different components of the bone marrow based on the different information provided by the different characteristics of the MRI sequences. This article provides an overview of the MRI appearances of normal and abnormal bone marrow. We review the MRI features of normal developmental red marrow- to yellow-conversion, reconversion and physiologic conditions. We review the key imaging techniques used in assessing bone marrow pathology in MRI, including T1-weighted, T2-weighted, Dixon chemical shift imaging and diffusion-weighted imaging, as well as dynamic contrast-enhanced (DCE) MRI. It is discussed the bone marrow characteristics in the different morphological and functional MRI sequences from the normal or abnormal conditions such as; infiltration (metastases), proliferation [multiple myeloma (MM)], vascular edema/necrosis and postreatment changes. We show the different MRI features to differentiate physiological processes from pathological processes in order to provide effective diagnoses, as well as to evaluate the optimal therapeutic monitoring assessment. Insights from recent advancements in imaging technology and emerging MRI techniques are also discussed, providing a comprehensive overview of bone marrow MRI and its clinical implications. This review provides a useful tool for radiologist to decide normal or abnormal findings from the analysis of bone marrow MRI; in order to manage and take decisions that will depend on the imaging findings. The optimal analysis of bone marrow MRI requires knowledge of the physiology of the bone marrow to interpret properly the pathology and avoid diagnostic errors.

Keywords: Bone marrow; magnetic resonance imaging (MRI); metastases; red and yellow bone marrow.

Figure 1

Bone marrow reconversion. A 37-year-old male long-distance runner. Sagittal FSE T1 showing reconversion of the yellow marrow to red marrow in the platform region, vertebral epiphysis (arrows). FSE, fast spin echo.

Figure 2

Sagittal T1 of the spine showing central high signal in a hypointense focal area, indicative of fat, in relation to the rest of normal red marrow (arrow), “bull’s eye” sign.

Figure 3

Axial T2 of the lumbar spine showing nodular lesion with a more hyperintense peripheral halo in the vertebral body (arrow) due to edema, indicative of metastasis.

Figure 4

Chemical shift imaging and Dixon acquisition. Drawing shows the 4 images after Dixon acquisition. The signal intensities of the in-phase and opposed-phase images are added or subtracted to obtain a water-only or fat-only set of images, respectively. (A) A hypointense area on in-phase image that becomes with significantly lower signal on out-phase images and not as low in fat only images indicates high amount of microscopic fat consistent with a benign lesion. (B) A hypointense area on in-phase image that does not become with significantly lower signal on out-phase images and with lower signal in fat only images indicates low amount of microscopic fat consistent with a malignant lesion.

Figure 5

Coronal image in out-of-phase T1 sequence of both knees showing focal hyposignal in the bone marrow with a symmetrical distribution in the distal diaphysis of the femur (arrows) indicative of red marrow remains.

Figure 6

Osteolytic and osteoblastic vertebral metastases from prostate carcinoma. Osteolytic metastases with diffusion restriction are observed at the upper dorsal, L5 and sternal levels (arrows) and an osteoblastic metastasis in L2 (asterisk), which does not present diffusion restriction and is markedly hypointense on T1 (A) and STIR (B). In the diffusion sequence, no involvement of the blast vertebra is observed (asterisk) (C). STIR, short tau inversion recovery.

Figure 7

Benign and malignant edema on the ADC map. Lumbar MRI in a patient with known bone metastasis from breast cancer, currently presenting with acute low back pain. (A) Sagittal in FSE T1 showing multiple focal lesions, especially in L1 (short arrow) and diffuse edema in L5 (long arrow). (B) The corresponding sagittal STIR shows a more diffuse edema at both levels that is difficult to differentiate whether infiltrative or non-infiltrative. (C) Sagittal diffusion at b=0 mm²/s and (D) at b=800 mm²/s showing the persistence of hypersignal from the lesion at the level of L1 (short arrow) and lower signal at L5 (long arrow). (E) The sagittal section on the ADC map confirms the hyposignal in L1 (short arrow) with an ADC value of 0.7×10⁻³ mm²/s and hypersignal in L5 with an ADC value of 1.6×10⁻³ mm²/s. The lesion in L1 is due to a metastasis and in L5 due to an insufficiency fracture, where the sagittal FSE T1 image (A) shows a subcortical horizontal line (arrow), which justifies the current symptoms. ADC, apparent diffusion coefficient; MRI, magnetic resonance imaging; FSE, fast spin echo; STIR, short tau inversion recovery.

Figure 8

MRI patterns of multiple myeloma. (A) Sagittal FSE T1 showing nodular lesion in L4 (arrow) in relation to focal pattern, (B) sagittal FSE T1 showing diffuse infiltration of the bone marrow in the cervical vertebral bodies in relation to diffuse pattern, with superimposed osteoarthritis from C3 to C6, (C) sagittal on FSE T1 showing mottled, variegated or salt and pepper pattern; represented by diffuse micronodular lesions in the bone marrow and (D) sagittal in FSE T1 showing micronodular pattern in the vertebral bodies of the lumbar spine, similar to that observed in L4 (long date) together with diffuse infiltration of S1 (short arrow); in relation to combined-mixed pattern. MRI, magnetic resonance imaging; FSE, fast spin echo.

Figure 9

Transient edema (transient osteoporosis). Coronal T1 image of a pregnant woman with diffuse edema of the left femoral head and neck with complete resolution 3 months after unloading measurements (right image).

Figure 10

Sixty-one-year-old man with acute low back pain. (A) Detection of lumbar metastasis in sagittal FSE T1 (white arrow) from unknown primary tumor. (B) The primary tumor detection and staging study on coronal multiplanar reconstruction image with gray scale diffusion contrast inversion of the whole body shows the primary detection of prostate neoplasia (thick arrow in A), bone metastases of the spine (arrowheads), right pelvis (short arrow) and multiple lymphadenopathy at the retroperitoneal and thoracic level (long arrows). (C) Control coronal MR image of multiplanar reconstruction with contrast inversion in gray scale in whole-body diffusion at 4 months after treatment with hormonal blockade and radiotherapy demonstrates absence of lesions, in relation to complete response. (D) Sagittal FSE T1 image in the initial study showing involvement of D4 and L3 (arrows). (E) Sagittal in FSE T1 at 4 months post-treatment in radiotherapy and hormonal blockade shows morphological stability (arrows), while diffusion (C) allows assessing the complete response due to the absence of diffusion restriction (resolution of the lesions in B, arrowheads), in correlation with the clinical response of PSA decrease. The solely morphological criterion would have incorrectly interpreted the therapeutic response. FSE, fast spin echo; MR, magnetic resonance; PSA, prostate-specific antigen.