MRI of Skeletal Muscle - Traumatic Injuries

Transcription

1 Acta Radiológica Portuguesa, Vol.XXII, nº 86, pág , Abr.-Jun., 2010 MRI of Skeletal Muscle - Traumatic Injuries Zehava S. Rosenberg Department of Radiology, NYU Hospital for Joint Diseases MRI OF SKELETAL MUSCLE Traumatic injuries Zehava S. Rosenberg MD New York University Medical School INDICATIONS FOR MRI Most injuries - self limited, MRI rarely indicated Assess extent of injury in high performance athletes Differentiate from other pathology, esp neoplasm Obscure muscle pain, severe cases of DOMS Surgical vs. conservative treatment MRI OF TRAUMATIC MUSCLE INJURIES Hernia Myositis ossificans DOMS Tears, strains Infarct Compartment syndrome Rhabdomylosis Denervation Contusion Hematoma Fluid sensitive - Increased signal T1 normal or mixed TECHNIQUE Axial - large FOV, may compare to uninvolved side Coronal if ROI is medial- lateral Sagittal if ROI anterior posterior FSE IR, w largest FOV, less than 2 min - light bulb effect Axial T1, Fat suppressed T2 T1 same plane as STIR (fat vs. hemorrhage) IV gadolinium - rarely necessary, may help distinguish hematoma from neoplasm OBJECTIVES Normal skeletal muscle anatomy Pathophysiology of traumatic muscle injuries Assess various traumatic disorders of muscle Pearls for distinguishing various traumatic muscle disorders MUSCLE FIBER TYPES Type I: slow-twitch fibers " Slow contraction " Greater endurance, resistant to fatigue " More mitochondria, capillaries " Chicken legs dark meat Type II: fast-twitch fibers " Fast contractions " Intense activity of short duration " Generate more tension, more force From: Crazy Cluck Chicken ARP!133

2 Muscle Function Skeletal muscles - varying ratios of slow, intermediate & fast twitch fibers With endurance training ratio may shift to more slow twitch Low intensity exercise more type I fibers are selected Intense exercise - more type II fibers are recruited MRI of DOMS Increased T2 signal " Muscle edema, perifascial fluid collections Signal resolves up to 80d Resembles grade I muscle strain DDX: " Sx delayed w DOMS HJD radiologist a few days post intense exercise Muscle Physiology Major skeletal muscle function contraction induces joint motion Concentric contraction - muscle shortens under loading Isometric contraction - muscle length remains constant under loading Eccentric contraction - muscle lengthens under loading " Highest muscle tension HJD radiologist a few days post intense exercise TRAUMATIC MUSCLE INJURIES DOMS Contusion Hematoma Laceration Strain (tear at MTJ) Myositis Ossificans Herniation Compartment syndrome Athletic runner Courtesy Jenny Bencardino DELAYED ONSET MUSCLE SORENESS (DOMS) Pain, temporary loss of strength 1-2 d post exercise Resolves in 5-7 days More common, more severe in deconditioned individuals Etiology: disruption of connective tissue, muscle attachment, IM fluid, pressure Ballet dancer 134! ARP

3 LACERATION Direct injury secondary to penetrating trauma Resolution with residual scar and little muscle rejuvenation Transverse defect composed of hemorrhage and fluid Diff Dx: History, usually transverse gap MR features - size, signal due to edema hemorrhage, hematoma Focal abnormality, muscle integrity usually not violated Not necessarily by MTJ Differential diagnosis: History, location, vastus intermedius MUSCLE CONTUSION KICKED by HORSE Laceration Direct injury due to penetrating trauma Resolution w residual scar & little muscle rejuvenation Transverse defect composed of hemorrhage, fluid Diff Dx: History, usually transverse gap 17 drunk, cut by broken bottle in bar fight MUSCLE CONTUSION KICKED by HORSE MR features - size signal related to edema hemorrhage, hematoma Differential diagnosis: History!!!! " Focal abnormality, muscle integrity usually not violated " Not necessarily by Direct trauma, blunt object Capillary rupture, interstitial hemorrhage, hematoma Pain, spasm, swelling, stiffness Normal muscle function MUSCLE CONTUSION Acute, painful, stretch induced injury at MTJ Sudden violent force Most common in lower extremity Prior injury Age Steroid use MUSCLE STRAIN MUSCLE CONTUSION MUSCLE STRAIN MR features - size, signal due to edema hemorrhage, hematoma Focal abnormality, muscle integrity usually not violated Not necessarily by MTJ Differential diagnosis: History, location, vastus intermedius KICKED by HORSE Long, fusiform, superficial muscles Predominantly type II fibers (fast twitch) Eccentric contraction (lengthen while contract) Muscles that cross more than one joint ARP!135

4 Muscles that undergo strains " Rectus femoris " Hamstrings " Gastrocnemius " Sartorius " Gracilis " Biceps (elbow) " Pectoralis GRADING OF MUSCLE STRAINS Grade I - stretch injury, minor degree of tear, no permanent defect Grade II - partial tear, clinical partial loss of muscle function (strength) Grade III - complete tear, extensive disruption of fibers, nearly complete loss of function Myotendinous unit injuries Chain: Bone (apophysis) - tendon muscle tendon - bone Weakest link depends on age: Children Apophysis Young adults MT junction Older adults - Tendon MRI OF MUSCLE STRAIN Grade I - slightly enlarged muscle, feathery increased signal, edema vs. hemorrhage, perifascial fluid collection Grade II - feathery changes of Grade I, hematoma at MTJ, partial defect, lax, irregular tendon Grade III - definite disruption of muscle fibers, retracted edges, gap - blood, hematoma Location of MTJ Focal, at junction of tendon & muscle Deep, at intra substance, long MTJ rectus, hamstrings TENNIS LEG MTJ injury Gastrocnemeius, plantaris, soleus 50+ individuals, weekend warrior, jumping, dancing Sudden onset of pain Diff dx: other causes of posterior calf pain " Achilles tear, ruptured Baker s cyst, DVT, MTS syndrome, compartment syndrome Conservative treatment MRI of TENNIS LEG Aponeurosis tear Edema, hemorrhage, hematoma tracking between muscles Proximal extent suggests plantaris tear Intact aponeurosis -?Ruptured BC TENNIS LEG RECTUS, HAMSTRING 136! ARP

5 Grade I strain in medial head of gastrocnemius, soleus Medial Gastrocnemius Tear ARP!137

6 Complications of Muscle Injury Compartment syndrome Hematoma Atrophy and fatty change Fibrosis/scar formation Compensatory hypertrophy (uncommon) Myositis ossificans Muscle herniation Calcific myonecrosis MUSCLE STRAIN VS.TENDON INJURY MTJ STRAIN Acute injury Result of macro trauma Violent force Occurs at MT junction Tendon is normal Produces immediate clinical signs & sx TENDON TEAR Chronic injury Repetitive micro trauma Sub maximal load Occurs at BT junction Tendon is degenerated Eventually produces clinical signs & sx Acute Compartment Syndrome intra compartmental pressure in a closed space ischemia and neuromuscular injury A-V gradient ischemia and necrosis Causes include FX, surgery, ST contusion, muscle rupture Anderson M et. al. AJR:173, December 1999 CHRONIC EXCERTIONAL COMPARTMENT SYNDROME Well conditioned athletes < 40 yo Repetitive loading or exertional activities Any compartment, but most common in anterior calf Exercise induced pain, relieved by rest Increased calf pressure at rest, greater post excercise Rx: Fasciotomy Post surgical 138! ARP

7 68 male w calcific myonecrosis, post surgical compartment syndrome as child Tumor vs. Hematoma 7 yo w synovial sarcoma 54 yo w hematoma MRI FEATURES OF HEMATOMA Common post MTJ injury Intramuscular, intermuscular May resorb in 6-8 wks Acute 1-4 days, low T1, T2 " Intracellular deoxyhemoglobin, methemoglobin Subacute - 5d - 3wks, months, bright on T1, T2 " Extracellular methemoglobin Chronic - wks to months, low T1, T2 " heterogeneous due to repeated bleed) " Pseudocyst encapsulated serous like fluid Hematoma - Fusiform, elongated Vastus intermedius common location 24 yo w vastus intermedius hematoma Fat containing tumors (hemangioma, angiolipoma, liposarcoma ) w T1, T2 signal may mimic hematoma Subactue hematoma bright signal on T1 must be distinguished from fat containing tumors 24 yo w vastus intermedius hematoma 53 f w hemangioma signal on T1, T2 54 female w hematoma & extensive soft tissue edema History is important Must exclude underlying tumor in setting of hematoma without significant trauma history Unusual location Malignant fibrous histiocytoma ARP!139

8 Lung met mimicking hematoma HEMATOMA VS. NEOPLASM HEMATOMA NEOPLASM Trauma, anticoagulant Fusiform Thick, non nodular wall Rim enhancement No trauma Round, oval Nodular wall Intralesional enhancing nodules No hemosiderin in wall Displaces MTJ Well defined, no edema Hemosiderin in wall At MTJ Surrounding edema DIFFICULT CASES - FOLLOW UP MRI OR BIOPSY Traumatic atrophy : may mimic end stage denervation Look for tendon, MTJ, aponeurosis abnormalities ATROPHY POST GASTROCNEMIUS TEAR Decreases elasticity of muscle Predisposes to repeat tears Longitudinal in hamstrings, rectus femoris Rx: PT, deep massage, resection Scar formation/ fibrosis Early scar formation in rectus 140! ARP

9 Fibrous encasement, scarring of rectus femoris MYOSITIS OSSIFICANS (MO) Young adults, children Common in Quadriceps & brachialis Traumatic event - localized repair, tissue maturation to cartilage and bone 3 histologic zones: " central - proliferative, " intermediate - osteoblasts, immature osteoid, peripheral " mature bone MUSCLE INJURIES AS MIMICS OF TUMORS Muscle retraction due to MTJ & tendon tears may present clinically as mass More common in superficial muscles Rectus femoris, hamstrings, adductors Old adductor longus tear presenting as a mass MYOSITIS OSSIFICANS (MO) MR features - early & intermediate, non specific - can mimic soft tissue sarcoma, CT may be useful Surrounding soft tissue edema in MO good distinguishing feature from sarcoma STIR and post C ARP!141

10 30 yo w myositis ossificans MUSCLE HERNIATION Focal muscle protrusion via post surgical, post traumatic fascial defect Weak fascia,! intracompartmental pressure Athletes, soldiers, blunt trauma Common in mid, lower leg (tibialis anterior, peroneus longus) Often asx, small, superficial, firm bulge at rest, prominent with muscle contraction MR - fascial defect, irregular muscle contour, edema Dynamic MR imaging vs US 30 yo w myositis ossificans 70 f with vastus lateralis hernia post resection of sarcoma 4 yrs ago 47 f presented w suspected mass Large myositis ossificans in 18 m post surgical fascial defect & peroneus longus hernia 142! ARP

11 THANK ARP!143