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Skeletal muscle, measuring up to 60% of the total protein stores, comprises the most abundant tissue in the human body of young adults [1,2].\u00a0Skeletal striated muscle, also referred to by its Latin name, muscularis striatus skeletalis, is a complex organ, which contains multiple bundles of cells known as muscle fibers.\u00a0Muscle fibers comprising the basic structural element of skeletal muscle are cylindrical and are composed of myofibrils, which, in turn, are composed of the contractile proteins actin and myosin.\u00a0As a major functional unit surrounding bones, skeletal muscles orchestrate all coordinated body movements that enable our activities of daily living, and, as such, any offense in muscle mass can be responsible for considerable disability.\u00a0Because patients with muscle derangements may present with non-specific symptoms of myalgia (pain), weakness, and fatigue, abnormalities in muscle are often overlooked or underestimated as a source of pathology.\u00a0Not infrequently, clinical assessment of the integrity and performance of muscle is difficult owing to complex compartmental anatomy and numerous anatomic variations, making a presumptive diagnosis of skeletal muscle disease rely strongly on a clinical imaging correlation.\u00a0Despite advanced imaging methods for muscle disease, biopsy remains the cornerstone of diagnosis that proves valuable in challenging, or indeterminate, cases [3-6].<\/p>\n
Myopathy is associated with an infinite variety of infectious, inflammatory, traumatic, neurological, genetic, neoplastic, and iatrogenic conditions that can cause pain and disability, and, as such, specific imaging is required [3-5].\u00a0Although diverse, some diseases offending muscle share similar imaging appearances, whereas others present distinct patterns of imaging abnormality. Magnetic resonance (MR) imaging is well suited for the direct and detailed assessment of soft tissue, including muscle.\u00a0Key MR imaging findings of myopathy generally fall into one of three cardinal patterns: muscle edema, fatty infiltration, and mass lesion [6].\u00a0To address the clinical heterogeneity of muscle abnormalities, we revisit the fundamental MR signal alterations associated with common and uncommon muscular derangements.\u00a0Importantly, this article aims to provide clinicians with a succinct and practical imaging guide for diagnosing myopathy.<\/p>\n
A summary of the imaging techniques used in the analysis of several primary and systemic disorders affecting skeletal muscle is provided in Table 1.<\/p>\n
| \nModality\n<\/td>\n | \nPros\n<\/td>\n | \nCons\n<\/td>\n<\/tr>\n |
| \nRadiography\n<\/td>\n | \nInitial assessment of suspected abnormality\n<\/td>\n | \nSuboptimal for deep-seated or nonmineralized lesions\n<\/td>\n<\/tr>\n |
| \nAlerts for further imaging\n<\/td>\n | \nUnrewarding if complex anatomy\n<\/td>\n<\/tr>\n | |
| \nUltrasound\n<\/td>\n | \nEvaluation of superficial soft-tissue masses\n<\/td>\n | \nOperator dependent\n<\/td>\n<\/tr>\n |
| \nDifferentiation of solid from cystic lesions\n<\/td>\n | \nLimited reproduction of images\n<\/td>\n<\/tr>\n | |
| \nEvaluation of muscle size and echogenicity\n<\/td>\n | \u00a0<\/td>\n<\/tr>\n | |
| \nAssessment of musculotendinous junction integrity\n<\/td>\n | \u00a0<\/td>\n<\/tr>\n | |
| \nSimultaneous assessment of neurovascular structures\n<\/td>\n | \u00a0<\/td>\n<\/tr>\n | |
| \nCT\n<\/td>\n | \nAssessment of muscle morphology and attenuation\n<\/td>\n | \nLimited contrast resolution for muscle\n<\/td>\n<\/tr>\n |
| \nCharacterization of soft-tissue mineralization\n<\/td>\n | \nUse of ionizing radiation\n<\/td>\n<\/tr>\n | |
| \nGuides percutaneous soft-tissue biopsy\n<\/td>\n | \u00a0<\/td>\n<\/tr>\n | |
| \nMRI\n<\/td>\n | \nEvaluation of muscle morphology and intrinsic characteristics\n<\/td>\n | \nLess sensitive for soft-tissue mineralization\n<\/td>\n<\/tr>\n |
| \nDetection of muscle edema, fatty infiltration, mass lesion\n<\/td>\n | \nSusceptible to motion artifacts, pacemakers\n<\/td>\n<\/tr>\n | |
| \nAssessment of bone marrow and neurovascular structures\n<\/td>\n | \u00a0<\/td>\n<\/tr>\n<\/table>\n\nTable<\/span>\n1: \nA 23-year-old man presented with pain in the right shoulder after an intense weight-lifting workout. \n<\/h6>\n (A) Coronal short-tau inversion recovery image shows abnormal high signal intensity in infraspinatus muscle, without obvious architectural distortion of muscle. Edema in a \u201cfeathery\u201d pattern is tracking along muscle fascicles (asterisk) and around epimysium (arrowheads) between cranial and central parts of the infraspinatus.<\/p>\n (B) Axial fat-suppressed fast spin-echo T2-weighted MR image reveals hyperintense fluid within the muscle belly (arrowheads), consistent with a strain of the infraspinatus muscle. Note extensive edema at the myotendinous junction (arrow) of the torn infraspinatus tendon.<\/p>\n
\nFigure<\/span>\n3: \nA 65-year-old man with generalized bone and soft-tissue echinococcosis of the left hemipelvis and the thigh. \n<\/h6>\n Coronal T2-weighted (A) and short-tau inversion recovery (B) images show diffuse edema in the vastus intermedius and lateralis muscles (VM) coupled with marked atrophy of the adductor (AM) muscles, in contrast with the normal appearance of the opposite side.<\/p>\n (C) Axial short-tau inversion recovery image through the thigh shows the denervation of the vastus muscles (VM) owing to the inflammation of the femoral nerve (thick arrow). A large parasitic cyst (c) growing within the adductor magnus muscle causes compression of the sciatic nerve (arrow), and atrophy of muscles in the posterior compartment of the thigh (arrowheads).<\/p>\n
\nFigure<\/span>\n5: \nA 48-year-old man after remote below-knee amputation. \n<\/h6>\n (A) Sagittal T1-weighted MR image shows increased signal consistent with fatty infiltration of atrophied semimembranosus (arrowheads) and gastrocnemius muscles (asterisk) due to chronic disuse.<\/p>\n (B) Axial T2-weighted MR image shows fatty infiltration pattern involving semimembranosus (arrowhead), semitendinosus (arrow), and biceps femoris (thick arrow) muscles.<\/p>\n (C) Corresponding T2-weighted MR image with fat suppression reveals a lack of high-signal-intensity fat within infiltrated muscles.<\/p>\n
\nFigure<\/span>\n7: \nA 34-year-old male with muscle weakness after receiving prolonged treatment with corticosteroids for Crohn\u2019s disease. \n<\/h6>\n (A) Coronal T1-weighted MR image reveals overt generalized atrophy of muscles around the hip and thigh (arrows). Note the increased accumulation of fat in the thigh (arrowhead).<\/p>\n (B) Corresponding axial T1-weighted MR image shows marked fatty infiltration of the gluteal muscles (arrowheads). The regional fat depot is seen in the buttock (asterisk).<\/p>\n Atrophy and fibrofatty infiltration may result in muscle contraction and stiffness, which may predispose weakened muscles to further injury during muscle exertion.\u00a0On the contrary, some inherited myopathies (metabolic myopathy, dystrophinopathies, sarcoglycanopathies) may manifest with local or generalized muscle hypertrophy or pseudohypertrophy (Figure 8).<\/p>\n
\nFigure<\/span>\n9: \nA 69-year-old diabetic man with pyelonephritis. \n<\/h6>\n (A-C) Coronal T1- (A), T2- (B), and enhanced, fat-saturated T1-weighted (C) MR images display intramuscular abscess (arrow) of the psoas muscle.<\/p>\n
\nFigure<\/span>\n11: \nA 27-year-old male with a laceration anterior to the thigh. \n<\/h6>\n (A) Sagittal T1-weighted MR image through the thigh shows acute hematoma (arrows) with intermediate signal intensity in injured vastus intermedius muscle. Note the extensive hemorrhage infiltrating the muscle adjacent to hematoma (arrowheads).<\/p>\n (B) Axial fat-suppressed fast spin-echo T2-weighted MR image reveals defect (arrowhead) in anterior musculature between sartorius (S) and rectus femoris (R) overlying hematoma (arrow) within enlarged vastus. Findings are consistent with muscle laceration with the formation of hematoma from a stab wound. Note perifascial edema (thin arrow).<\/p>\n
\nFigure<\/span>\n13: \nA 58-year-old man with advanced metastatic disease due to the spread of soft-tissue sarcoma. \n<\/h6>\n (A) Coronal high-resolution T2-weighted MR image shows infiltration of the bone (ischium) (thin arrow) and the piriformis muscle (arrow).\u00a0 Note the descending sciatic nerve (arrowhead) adjacent to infiltrated muscle, responsible for sciatica.<\/p>\n (B) Coronal T1-weighted MR image with fat saturation after the administration of gadolinium-containing contrast agent depicts ample enhancement of metastatic deposits in both the muscle (arrow) and bone. Abnormal enhancement of the sciatic nerve is also seen.<\/p>\n As a general rule, discrete mass lesions that disrupt normal muscle architecture indicate an aggressive or recurrent tumor with an ominous prognosis.\u00a0MR imaging may afford a detailed analysis of the consistency of a mass lesion that reflects the histology of a given pathologic process.\u00a0In this regard, MR imaging may definitely enable a thorough pre-biopsy investigation of the nature of a mass or mass-like lesion providing meaningful clues to diagnosis.<\/p>\n Imaging differential diagnosis<\/h4>\nWithin the broad spectrum of myopathies, knowledge of the characteristic MR imaging patterns of muscle disease is a requisite for maximizing diagnostic accuracy [27].\u00a0Although these patterns may be diagnostic in the appropriate clinical context, additional MR imaging alterations in muscle may include abnormal low signal intensity on T2-weighted images, representing calcification, fibrosis, hemosiderin deposition, gas, and foreign bodies. The presence of methemoglobin in muscle, proteinaceous material, melanin, or gadolinium-based contrast material may account for high T1 signal intensity in muscle [28].<\/p>\n Because the potential causes for abnormal signal intensity in muscle are diverse, recognition of the three basic patterns may help narrow the differential diagnosis or suggest a specific diagnosis. The \u201cmuscle edema pattern\u201d is the most common pattern of altered muscle signal intensity and may be observed with trauma, rhabdomyolysis, vascular insults, subacute denervation, and infectious\/inflammatory myopathies. The \u201cfatty infiltration pattern\u201d is often associated with atrophy and can be seen in cases of hereditary myopathy, chronic muscle injury, disuse, and corticosteroid use. The \u201cmass lesion pattern\u201d is commonly seen with neoplasms, infection, traumatic injuries (myositis ossificans), and muscular sarcoidosis. Assignment of a muscle disorder to one of the three major MR imaging-based patterns may simplify the diagnostic approach for myopathy. However, it should be emphasized that in some instances, the MR imaging findings of muscle disease may reflect the underlying gross pathologic changes rather than provide features for specific imaging diagnosis, and, as such, a wide range of clinical differential diagnoses may eventually need to be entertained.<\/p>\n","protected":false},"excerpt":{"rendered":" Skeletal muscle, measuring up to 60% of the total protein stores, comprises the most abundant tissue in the human body of young adults [1,2].\u00a0Skeletal striated muscle, also referred to by its Latin name, muscularis striatus skeletalis, is a complex organ, which contains multiple bundles of cells known as muscle fibers.\u00a0Muscle fibers comprising the basic structural […]<\/p>\n","protected":false},"author":1,"featured_media":3586,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[18],"tags":[19],"class_list":{"0":"post-3585","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-ciatica","8":"tag-ciatica"},"_links":{"self":[{"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/posts\/3585","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/comments?post=3585"}],"version-history":[{"count":1,"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/posts\/3585\/revisions"}],"predecessor-version":[{"id":3587,"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/posts\/3585\/revisions\/3587"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/media\/3586"}],"wp:attachment":[{"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/media?parent=3585"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/categories?post=3585"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/americanchiropractors.org\/es\/wp-json\/wp\/v2\/tags?post=3585"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}} |
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