Abnormal Signal Intensity in Skeletal Muscle at MR Imaging: Patterns, Pearls, and Pitfalls

Abstract

Abnormal signal intensity within skeletal muscle is frequently encountered at magnetic resonance (MR) imaging. Potential causes are diverse, including traumatic, infectious, autoimmune, inflammatory, neoplastic, neurologic, and iatrogenic conditions. Alterations in muscle signal intensity seen in pathologic conditions usually fall into one of three recognizable patterns: muscle edema, fatty infiltration, and mass lesion. Muscle edema may be seen in polymyositis and dermatomyositis, mild injuries, infectious myositis, radiation therapy, subacute denervation, compartment syndrome, early myositis ossificans, rhabdomyolysis, and sickle cell crisis. Fatty infiltration may be seen in chronic denervation, in chronic disuse, as a late finding after a severe muscle injury or chronic tendon tear, and in corticosteroid use. The mass lesion pattern may be seen in neoplasms, intramuscular abscess, myonecrosis, traumatic injury, myositis ossificans, muscular sarcoidosis, and parasitic infection. Some of these conditions require prompt medical or surgical management, whereas others do not benefit from medical intervention. The ability to accurately diagnose these conditions is therefore necessary, and biopsy may be required to establish the correct diagnosis. Clues to the correct diagnosis and whether biopsy is necessary or appropriate are often present on the MR images, especially when they are correlated with clinical features and the findings from other imaging modalities.

A 48-year-old man with chronic right shoulder pain and weakness after a fall: diagnosis and discussion

“…If normal innervation is restored, MR findings ultimately return to normal. However, if innervation is not restored, atrophy with fatty infiltration develops after a period of months, indicating irreversible muscle injury [6]. Our case illustrates this MR appearance of chronic axillary nerve injury.…”

Intramuscular migration of calcium hydroxyapatite crystal deposits involving the rotator cuff tendons of the shoulder: report of 11 patients

“…The most common denervation injuries involving the muscles of the rotator cuff are cervical radiculopathy, brachial neuritis (Parsonage-Turner syndrome), and suprascapular nerve compression at the spinoglenoid notch [6,[20][21][22][23]. Denervation edema, unlike intramuscular HADD-related edema, results in a mild increase in signal intensity that uniformly involves the entirety of the affected muscles and is not associated with perimuscular fluid accumulation [20,23,24]. Diffuse muscle edema may also be seen in the context of myositis, either pyogenic or idiopathic.…”

“…Diffuse muscle edema may also be seen in the context of myositis, either pyogenic or idiopathic. The clinical history of infection is key to differentiate it from intramuscular HADD [24]. The most reliable way to distinguish these entities from intramuscular HADD through imaging, however, is achieved through the documentation of rotator cuff calcifications on radiographs or CT.…”

G-CSF for Imatinib-induced neutropenia

“…6 The clinical course of our patient excluded these causes from the diagnosis. The mechanism of edema and fluid retention remains unknown.…”

“…4 The percentage of peripheral blood or marrow blasts has been identified as the only significant variable for the development of grade 3 or 4 neutropenia for patients on Imatinib therapy. 6 The presence of significant cytopenia after 6 months of Imatinib treatment is a bad prognostic factor. The development of grade 3 or 4 cytopenia in patients with chronic phase CML treated with Imatinib is associated with a significantly higher rate of progression to accelerated phase or blastic phase CML.…”