Whole-body magnetic resonance imaging (WBMRI) versus whole-body computed tomography (WBCT) for myeloma imaging and staging

Abstract

Myeloma-associated bone disease (MBD) develops in about 80–90% of patients and severely affects their quality of life, as it accounts for the majority of mortality and morbidity. Imaging in multiple myeloma (MM) and MBD is of utmost importance in order to detect bone and bone marrow lesions as well as extraosseous soft-tissue masses and complications before the initiation of treatment. It is required for determination of the stage of disease and aids in the assessment of treatment response. Whole-body low-dose computed tomography (WBLDCT) is the key modality to establish the initial diagnosis of MM and is now recommended as reference standard procedure for the detection of lytic destruction in MBD. In contrast, whole-body magnetic resonance imaging (WBMRI) has higher sensitivity for the detection of focal and diffuse plasma cell infiltration patterns of the bone marrow and identifies them prior to osteolytic destruction. It is recommended for the evaluation of spinal and vertebral lesions, while functional, diffusion-weighted MRI (DWI-MRI) is a promising tool for the assessment of treatment response. This review addresses the current improvements and limitations of WBCT and WBMRI for diagnosis and staging in MM, underlining the fact that both modalities offer complementary information. It further summarizes the corresponding radiological findings and novel technological aspects of both modalities.

Whole-Body Low-Dose Multidetector-Row CT in Multiple Myeloma: Guidance in Performing, Observing, and Interpreting the Imaging Findings

“…MM-related osteolysis is represented by small, focal, low-density lesions of trabecular bone without sclerotic boundaries (unless prior treatment) (Figure 6); these lesions are morphologically defined in literature by IMWG criteria as typical punched-out osteolytic areas with a diameter greater than or equal to 5 mm without reactive sclerosis of the surrounding bone [26]. CT is more sensitive compared to MRI in the detection of osteolytic bone lesions and better evaluates spinal stability in vertebral fractures; on the other hand, MRI is the reference standard method to detect bone marrow infiltration prior to bone fracture, as well as the various features of medullary involvement, ranging from focal and well circumscribed lesions to diffuse infiltration pattern; therefore, radiologists should always recommend MRI evaluation for those suspected small lesions that do not meet the strict abovementioned size criteria [27].…”

“…Endosteal scalloping is linked to focal resorption of the endosteum (the inner layer of the bone cortex), due to slow-growing medullary lesions (Figure 7), generating cortical thinning, more evident in the long bones. CT is more sensitive compared to MRI in the detection of osteolytic bone lesions and better evaluates spinal stability in vertebral fractures; on the other hand, MRI is the reference standard method to detect bone marrow infiltration prior to bone fracture, as well as the various features of medullary involvement, ranging from focal and well circumscribed lesions to diffuse infiltration pattern; therefore, radiologists should always recommend MRI evaluation for those suspected small lesions that do not meet the strict abovementioned size criteria [27].…”

“…In the case of para-medullary disease, soft tissue infiltration originates from a bone lesion, with the presence of extra-osseous lesions linked to skeletal involvement (Figure 8); PET-CT is the study of choice when extramedullary disease is suspected, and is also frequently used in patients with non-secretory MM [28]. Not all low-density trabecular bone lesions can be considered osteolysis: according to current literature, myelomatous lesions are those osteolytic lesions with plasma cell infiltration and a positive, tissue-like density, expressed as Hounsfield Units (HU): quantitative density measurements on WBLD-CT are necessary to distinguish between fatty hypodense bone marrow (ranging from −30 to −100 HU) and plasma cell infiltrates, which have a higher CT density (average 55 HU); moreover, the role of Dual-Energy CT (DECT) is nowadays growing in identifying bone marrow infiltration in non-osteolytic lesions, using the HU measurement references, as plasma cell infiltrates and fatty bone marrow have different attenuation values at CT acquisitions with different kVs [18,27,29]. Not all low-density trabecular bone lesions can be considered osteolysis: according to current literature, myelomatous lesions are those osteolytic lesions with plasma cell infiltration and a positive, tissue-like density, expressed as Hounsfield Units (HU): quantitative density measurements on WBLD-CT are necessary to distinguish between fatty hypodense bone marrow (ranging from −30 to −100 HU) and plasma cell infiltrates, which have a higher CT density (average 55 HU); moreover, the role of Dual-Energy CT (DECT) is nowadays growing in identifying bone marrow infiltration in non-osteolytic lesions, using the HU measurement references, as plasma cell infiltrates and fatty bone marrow have different attenuation values at CT acquisitions with different kVs [18,27,29].…”

“…Even when disease recurrence is suspected, based on serological tests, a WBLD-CT is recommended to assess the extent of bone lesions [4]. A well known disadvantage of CT examinations is represented by the use of ionizing radiation, even though low-dose protocols technical improvements, such as iterative reconstruction algorithms and dual-source CT scanners, considerably reduce the effective radiation dose [27].…”

“…On the other side, WBLD-CT imaging is not so efficient in detecting early bone marrow infiltration, when the bone destruction is not such as to cause frank osteolysis, particularly in the dense trabecular bone of spine and pelvis, as it is not easy to determine whether myelomatous cellular infiltration replaces the fatty bone marrow component, due to the CT density of these sites being a function of bone marrow composition and trabecular bone mineralization (Figure 10); in this setting, in case of negative WBLD-CT, a whole-body or spine and pelvic MRI should always be suggested in the radiological report as it is the most suitable imaging technique for patients with smoldering or asymptomatic MM, to exclude myelomatous lesions, to confirm the diagnosis of smoldering MM, or to find undetectable-CT lesions [27].…”