MRI OF MUSCLE DISEASESDR.SARATH MENON.R ,MD(Med.),DNB(Med.),MNAMS

DEPT.OF NEUROSCIENCES,

AIMS,KOCHI

INTRODUCTION – A PATTERN APPROACH

MRI -powerful tool to assess the severity, distribution, and progression of muscle injury and disease

Muscle’s response to a pathological insult is limited to only a few patterns on MRI, and non-specific.

MR appearances of muscle into 4 main pattern descriptors:

(1) distribution; (2) change in size and shape; (3) T1 signal (4) T2 signal

T1W sequences - muscle architecture and anatomy, in reference to normal surrounding fat.

Hemorrhage and abnormal fat deposition (e.g., fatty muscle atrophy or lipoma) assessed on T1W

T2W or STIR- characterize muscle edema.

Gradient echo-presence of hemosiderin, detect old injury

Contrast enhancement with gadolinium –-differentiating between a cystic or solid mass

-biopsy approach

-areas of acute degenerative activity

-identifying an abscess or necrotic tissue.

Normal muscle –intermediate/low signal intensity on all (MRI) pulse sequences

MRI OF NORMAL MUSCLE

NORMAL MUSCLE MRI

•Normal muscle is quite symmetrical. •The outside borders tend to be smooth and convex, so no bulging•Muscle should have low signal on all sequences•On T1-weighted images you will see fat in the muscle in very predictable patterns, with either linear, branching or feathery distributions, depending on the architecture of the muscle

PATTERN VARIABLE 1-DISTRIBUTION muscle presence location of findings in a muscle or muscle

compartment, contiguous vs. noncontiguous disease, symmetry, and involvement of the adjacent subcutaneous fat

and fascia

Diabetic muscle ischemia - muscles of the anterior thigh and posterior calf.

Denervation edema - asymmetric distribution, as changes reflect the distribution of a specific nerve

Diabetic neuropathy- involves the tibialis anterior & intrinsic muscles of the feet

Dermatomyositis/Polymyositis- muscles of the anterior thigh and posterior calf , lower >> upper limbs, and proximal > distal muscles

Inclusion-body myositis -the anterior thigh in isolation;

more distally particularly in the forearm flexor compartment

Duchenne & Becker muscular dystrophies, the pelvic girdle and proximal thighs - diffuse and symmetric or asymmetric

fashion

later stages, the calf and shoulder girdle are also involved.

relative sparing of the gracilis, sartorius, semimembranosus,and semitendinosus muscles

(a) Axial proton density and (b) coronal fat suppressed T2W images show decreased muscle bulk and hyperintense T2 signal in the anterior compartment of both thighs. The left side is more severely affected than the right. Mild edema is also seen in the left anterior subcutaneous fat.The differential considerations include dermatomyositis, polymyositis, and diabetes

Axial T1W image demonstrates complete fatty replacement of the deep head of the supinator muscle (arrow) implying chronic denervation change of posterior interosseous nerve entrapment syndrome.(denervation myopathy)

PATTERN VARIABLE 2: MUSCLE SIZE & SHAPE

T1W sequences- distinction between muscle & fat.

Gradient-echo sequences- demonstrating muscle -fascial interfaces

Abnormal muscle - normal, small, enlarged. comparison of contralateral or other surrounding muscles

A smaller muscle = muscle atrophy

Neighboring muscle –compensatory hypertrophy & bulk of the muscle group may remain the same.eg; Polio,Traumatic injury

If a muscle appears enlarged, T1W images-for abnormal fat deposition pseudohypertrophy.

eg.Duchenne/Becker

True muscle hypertrophy (fiber enlargement) - myotonia, acromegaly,Hoffman syndromes, sarcoidosis, amyloidosis,cysticercosis schistosomiasis

Changes in muscle shape - trauma(such as a hematoma or tear causing muscle fiber/ tendon retraction), herniation, or tumors.

An important caveat is a slow-flow vascular malformation,-disproportionately little mass effect and may therefore preserve muscle size and shape.

Most herniations occur in the leg, particularly herniations of the tibialis anterior.

Muscle herniating through a rent in the fascia is diagnostic on MRI

Chronic tear of the left medial gastrocnemius.(a) Axial T1W image demonstrates atrophy and patchy increased fat content in the left medial

gastrocnemius (arrow).There is a T1 hypointense intrafascial collection deep to the muscle (*). The left calf is larger than the right calf due to compensatory hypertrophy of the left soleus and deep posterior compartmental muscles; there is also increased fatty infiltration of the right calf muscles.

(b) Coronal fluid-sensitive image shows hyperintense signal of the collection (arrow), in keeping with a resolving hematoma or seroma

PATTERN VARIABLE 3- T1W SIGNAL

altered muscle T1W signal -always increased signal (T1 shortening) from fat.

Hemorrhage in the methemoglobin state, proteinaceous fluid, early calcinosis (hydroxyapatite deposition disease, myositis ossificans, & calcium pyrophosphate dihydrate deposition disease).

T1W imaging patterns include: (1) patchy fat or marbling, representing early

disease (2) complete fatty replacement of the muscle (3) focal fat or scar (4) post-traumatic hemorrhage; (5) loss of marbling from a mass or tumor

recurrence.

Patchy Fat/Marbling. Patchy fat replacement of muscle- an early stage of

completefatty replacement; it is seen in disease cause muscle edema

Vascular Malformations. Patchy fat can also be seen with intramuscular vascular

malformations

High flow AVM - a tangle of flow voids on T1W and T2W images & hyperintensity on flow-sensitive gradient-echo images

Low-flow AVM with venous components -serpentine structures with high T2W and intermediate T1W signal intensity; internal septations and striations may be present.

Lymphatic components of vascular malformations appear cystic and may demonstrate fluid–fluid levels.

Vascular malformation. (a) Axial T1W image demonstrates asymmetric enlargement of the left gluteus maximus and medius muscles. There is mild increased signal intensity, disruption of normal fatty septae, and a nodular contour at the interface of the muscle with the subcutaneous fat. (b) Fat-saturated T2W image demonstrates corresponding prominent increased signal within the mass similar to slow flow veins or fluid, which crosses myofascial planes between the left gluteus maximus and medius muscles.

Complete Fatty Replacement. End-stage result of patchy fatty replacement complete old tendon tear; denervation including diabetic

motor neuropathy; end-stage or burned-out dermatomyositis/polymyositis;long-standing disuse (e.g., immobilization); muscular dystrophies; and congenital myopathies

Muscular Dystrophy Increased T1 signal = fatty infiltration , initially in

gluteus maximus & adductor magnus,followed by quadriceps, rectus femoris,and biceps femoris.

Signal changes spare gracilis, sartorius, semimembranosus, and semitendinosus,which may hypertrophy

In the calf, the gastrocnemii are affected more severely than other muscles.

MUSCULAR DYSTROPHY

On the T1-weighted image only the posterior muscles contain normal fat. On the T2-weighted image there is edema of the quadriceps, which is a sign of early muscular dystrophy

Focal Fat. Lipoma- demonstrates pure fat signal on all pulse

sequences vascular malformation - curvilinear vascular

channels surrounded by fat scar tissue secondary to an old injury; or myositis

ossificans

Coronal T1W image of the right hand shows a well circumscribed, homogeneous fatty mass in the abductor pollicis brevis, displacing normal muscle tissue, a

benign lipoma.

MYOSITIS OSSIFICANS Vary with evolutionary phase of the mass Acute-well defined heterogenous signal intensity rim enhancement and muscle edema D/D- abscess,necrotic tumor,sarcoma

Subacute- iso-hyper intense T1W

Chronic – sharply marginated,no edema T1W/T2W- fat signal seen centrally = bone

marrow Hypointense rim corresp. Cortical bone

Myositis ossificans/heterotopic ossification. (a) Axial unenhanced CT image of the proximal left thigh demonstrates a well defined mass with peripheral calcification in the posterior subcutaneous tissues. (b) Axial T1W image shows a hypointense rim corresponding to the calcification with higher signal centrally relative to the thigh musculature Axial (c) proton density-weighted and (d) T2-weighted images with fat saturation show high signal centrally

and peripheral low T2 signal supporting chronic hemosiderin deposition or calcification.

Focal Hemorrhage/Hematoma Parenchymal hemorrhage little mass effect and exhibits a hyperintense lacy, feathery

appearance on STIR or fat-suppressed T2W sequences.

Subacute intramuscular hematoma. Axial T1W image demonstrates a hematoma in the right vastus intermedius (arrow). There is a hypointense rim with more hyperintense T1 signal centrally, corresponding to encapsulated methemoglobin in the collection. Although a hypointense rim is also seen with chronic hematomas, the presence of methemoglobin ischaracteristic of a subacute hematoma

Loss of Marbling. Hyperintense fat interposed between fibers gives

muscle its characteristic marbled appearance on T1.

Loss of this marbled appearance - ominous finding- raises suspicion for tumor

PATTERN VARIABLE4-T2W SIGNAL Muscle edema -hyperemia, congestion, post

traumatic, and tumor infiltration (tumorigenic),

Muscle edema into 6 patterns seen on T2W images:

(1) patchy focal edema (2) patchy edema throughout a single muscle (3) diffuse edema in a single muscle (4) edema in adjacent muscles (5) symmetric edema in non adjacent muscles (6) asymmetric edema

FOCAL EDEMA

post traumatic, either secondary to incomplete muscle

strain, the myotendinous junction Contusion-where the edema is located

superficially or at the muscle–bone interface

MUSCLE STRAINS 3 grades Grade1- T2W hyper at myotendinous junction TIW will be normal Grade 2- Grade1 + heamatoma

Grade 2 strain of the left hamstring tendon from its origin at the ischial tuberosity. (a) Sagittal proton-density weighted image of the left thigh shows retraction of the muscle(semitendinosus) belly distally (*). Some tendinous fibers remain intact (arrow). (b) Coronal and (c) axial STIR images demonstrate a large complex hematoma surrounding the central tendon (arrows). (d) Distally, the retracted left hamstring muscles demonstrate diffuse edema on this axial T2W image with fat saturation, suggesting intramuscular hemorrhage.

GRADE 3

Complete disruption of myo tendinous junction

MRI –disrupted muscle fibres with extensive edema(diffuse edema)

Inter/intramuscular heamtoma+

PATCHY EDEMA IN A SINGLE MUSCLE.

trauma -muscle strains and contusions- focal muscle or diffuse edema;

pyomyositis, - (typically edema in adjacent muscles)

diabetic myopathy- - denervation myopathy (typically diffuse

edema in a single muscle); - diabetic muscle ischemia/infarction

(symmetric /asymmetric edema in either a single muscle or multiple non adjacent muscles).

DIFFUSE EDEMA IN A SINGLE MUSCLE

Acute focal atrophy such as a complete (grade 3) muscle strain or acute denervation

DENERVATION RELATED MYOPATHY Hyperintense signal STIR/ T2W – due increase EC

space Post contrast enhancement T1W Long standing, atrophy,fatty replacement – T1W

Denervation related atrophy of left-side quadriceps femoris muscle. Axial STIR image shows both atrophy and residual muscle edema in subacute phase of intraoperative damage of deep branch of femoralnerve (arrow)

EDEMA IN ADJACENT MUSCLES

deep venous thrombosis compartment syndromes, eosinophilic myositis, pyomyositis, peripheral neuropathy(may not be entirely

adjacent), Vascular malformations Radiation, Lymphoma.

COMPARTMENT SYNDROME

T2W –subfascial hyper intensity within & between

adjacent muscles T1W- enlarged muscles & petechial

hemorrhage Contrast fatsat T1W- - avid enhancement in early phase - enhance peripherally,central

ischemia,necrosis in late phase

Bilateral compartment syndrome. (a) Coronal STIR and (b) axial fat-suppressed T2W images show extensive, patchy hyperintense T2 signal within and between muscles of the anterior compartments bilaterally. (c) Axial postcontrast fatsaturated T1W image shows peripheral enhancement of the anterior muscles and lack of central enhancement, in keeping with reduced perfusion and myonecrosis.

PYOMYOSITIS Buttocks,pelvis,thighs Early phase T2W/STIR- hyper intensity TIW-muscle enlarged,loss of

marbling,hyperintense

Late phase (abscess formation) T2W- hyperintense TIW- hypointense, wall- hyperintense Contrast T1W-ring enhancement with edema

pyarthrosis in right hip (arrowhead). Coronal STIR image shows focal secondary infectious myositis (arrow) in right quadriceps muscle adjacent to infected hip joint. At this time, there is no abscess formation

T1-weighted image with fatsat post contrast Fluid collections within the enhancing muscle in a patient with pyomyositis

focal myositis presenting as painful swelling of right thigh.A and B, Coronal STIR (A) and fat-saturated gadolinium enhancedT1-weighted (B) images show increased signal in focal distribution along rectus femoris muscle on right, suggestive of focal nodular myositis(arrows).

SYMMETRIC EDEMA IN NONADJACENT MUSCLES.

usually symmetric muscles polymyositis and other inflammatory

myopathies, delayed-onset muscle soreness (DOMS) Diabetes Drug induced

INFLAMMATORY MYOPATHY

MRI-excellent tool- early diagnosis- Severity and extent of active disease- Guidance for muscle biopsies- Monitoring progression- areas of fatty atrophy

POLYMYOSITIS/DERMATOMYOSISTIS

Thigh-vastus lateralis,intermedius Subcutaneous edema-DM Edema- sorrounding muscle/muscle group -TIW-ring like pattern Chronic-fatty atrophy

Juvenile DM- inter/intra muscular calcifications

polymyositis. Note diffuse edema and inflammation of obturator externus (arrowhead) and pectineus (arrow) muscles on axial STIR image

chronic polymyositis. Note advanced fatty atrophy,especially of quadriceps muscles (arrows), on unenhanced axial T1-weighted

dermatomyositis. Axial STIR image shows diffuse hyperintensity in some thigh muscles (arrowhead, vastus lateralis muscle).Note also increased signal in subcutaneous tissue septa (arrow) and skin thickening

Juvenile dermatomyositis. Whole-body STIR image shows multifocal patchy pattern of muscle edema andinflammation (arrows)

DRUG INDUCED

administration of statins. Note atrophy and hyperintensity of thigh muscles on axial STIR image (arrows).

INCLUSION BODY MYOSITIS Profound muscular atrophy Fatty atrophy More distal Extensors of knees,flexors of wrists,fingers Isolated anterior compartment of thigh

DELAYED ONSET MUSCLE SORENESS(DOMS) T2W/STIR –symmetric,feathery hyperintense signal Perifascial & intermuscular edema

60-year-old man days after excessive biking who has progressive myalgia in both legs, which is consistent with delayed

onset of muscle soreness.Note bilateral muscle edema on coronal STIR image involving especially quadriceps femoris muscles

Arrow in right thigh indicates vastus lateralis muscle; arrowhead shows edema of left vastus medialis muscle.

EDEMA IN NONADJACENT,NON SYMMETRIC MUSCLES.

Diabetic myonecrosis medications, rolling crush injuries rhabdomyolysis.

MUSCLE INFARCTION & DIABETIC MYONECROSIS

Lower extremity- anterior thigh & post.calf T1W- enlarged infarcted muscles,displaced fascial planes. - hyperintensity- hemorrhagic infarction T2W- diffuse.patchy,s/c,subfascial,intramuscular

edema Contrast T1W - diabetic muscle ischaemia - region of enhancement,non mass-like rim

enhancement with central non enhanced- myonecrosis -multiple non adjacent muscles

diabetic muscle disease/myopathy. (a) Axial fat-saturated T2W image of the calves -asymmetric, patchy edema in muscles of the lateral, anterior, and posterior right calf with neuropathic muscle disease. (b) Axial fat saturated proton density image of the left calf in type I diabetic with cellulitis, fasciitis, and ischemic myositis. There are skin thickening, subcutaneous edema, and focal fluid collections surrounding the superficial fascia of the calf (arrows). Interfascial fluid tracks between the gastrocnemius and medial soleus (arrowhead). Diffuse edema in the gastrocnemius and medial soleus without muscle enlargement favors ischemic myositis. Coronal (c) fat-saturated T2W and (d) contrast-enhanced T1W images of another patient demonstrate patchy muscle edema and enhancement throughout the left calf.

MUSCLE INFARCTION

Muscle ischemia/infarction. (a) Axial T2W image with fat saturation and (b) coronal STIR images show a focal area of abnormal, non–mass-like signal hyperintense to normal muscle in the right vastus lateralis. Contrast-enhanced (c) axial and (d) coronal T1W images with fat suppression show predominantly peripheral enhancement with subtle enhancement centrally.

In the lower leg there are four compartments: the anterior, deep and superficial posterior compartment and a small lateral compartment. On the left T1W-images of a patient one month post trauma.On the post-Gadolinium image the necrosis in the anterior and lateral compartment is seen. The posterior compartment is normal

RHABDOMYOLYSIS T2W/STIR- diffuse hyperintensity Gradient echo-hemosiderin-hemorrhagic

transfomation

diffuse edema of chest wall musculature as shown on coronal STIR imagealong pectoralis muscles.

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