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 Differential Diagnosis of Musculoskeletal Disorders

Categories of Soft-tissue Masses  !!navigator!!

  1. Neoplastic
    Incidence: 300÷100,000 / year; benign÷malignant = 100÷1
    1. benign (most frequent)
      1. Lipoma
      2. Hemangioma
      3. Desmoid tumor
      4. Ganglion cyst
      5. Pigmented villonodular synovitis
      6. Neurofibroma (5%)
      7. Lipoblastoma
    2. malignant
      Frequency: 1% of all cancers in adults, increasing with age
      1. Malignant fibrous histiocytoma
      2. Liposarcoma
  2. Inflammatory
  3. Traumatic
  4. Vascular

Superficial Soft-tissue Mass

  1. MESENCHYMAL TUMOR
    1. cutaneous
      1. Dermatofibrosarcoma protuberans
    2. subcutaneous
      1. Lipoma / liposarcoma
      2. Angioma (hemangioma, lymphangioma, mixed)
      3. Peripheral nerve sheath tumor
      4. Malignant fibrous histiocytoma
      5. Leiomyosarcoma
      6. Epithelioid sarcoma
    3. fascial
      1. Nodular fasciitis
      2. Fibromatosis
  2. SKIN APPENDAGE LESION
    1. Epidermal inclusion cyst
    2. Pilomatricoma
    3. Eccrine cystadenoma / hydrocystoma
      = cystic ectasia of dermal portion of eccrine duct
    4. Cylindroma (head, neck, scalp in women)
    5. Syringoma (eyelids, upper cheek)
  3. METASTATIC TUMOR
    ◊ 5–10% of all cancer patients develop skin metastases
    1. Carcinoma
      mnemonic: BLOCK
      • Breast
      • Lung
      • Ovary
      • Colon
      • Kidney
    2. Melanoma (in 30% of melanoma patients)
    3. Myeloma (in <5% of multiple myeloma patients)
  4. OTHER TUMORS & TUMORLIKE LESION
    1. Myxoma
      • homogeneous fluidlike signal intensity
    2. Lymphoma
    3. Granuloma annulare
  5. INFLAMMATORY LESION
    1. Cellulitis
      • = inflammation / infection of cutis + subcutis without gross suppuration
      • thickened skin with reticulated fluidlike SI
    2. Fasciitis
      • = inflammation / infection of fascia
      • fascial thickening + enhancement
    3. Adenitis
      • intermediate SI on non–fat-suppressed T2WI
    4. Abscess
      • = confined focal collection of pus or necrotic tissue + WBCs + bacteria
      • fluidlike signal intensity + rim of enhancement
    5. Phlegmon
      • = poorly defined region with edema-like pattern and indistinct margins

Histologic Classification of Soft-tissue Lesions  !!navigator!!

  1. FATTY
    1. Lipoma
    2. Angiolipoma
    3. Liposarcoma
  2. FIBROUS
    1. Fibroma
    2. Nodular fasciitis
    3. Aggressive fibromatosis / desmoid
    4. Fibrosarcoma
  3. MUSCLE
    1. skeletal muscle tumor
      1. Rhabdomyoma
      2. Rhabdomyosarcoma
    2. smooth muscle tumor
      1. Leiomyoma
      2. Leiomyosarcoma
  4. VASCULAR
    1. Hemangioma
    2. Kaposiform hemangioendothelioma
    3. Kaposi sarcoma
    4. Hemangiopericytoma
    5. Hemangiosarcoma
    6. Glomus tumor
    7. Myopericytoma
  5. LYMPH
    1. Lymphangioma
    2. Lymphangiosarcoma
    3. Lymphadenopathy in lymphoma / metastasis
  6. SYNOVIAL
    1. Nodular synovitis
    2. Pigmented villonodular synovitis
    3. Synovial sarcoma
  7. NEURAL
    1. Neurofibroma
    2. Neurilemmoma
    3. Ganglioneuroma
    4. Malignant neuroblastoma
    5. Neurofibrosarcoma
  8. CARTILAGE AND BONE
    1. Myositis ossificans
    2. Extraskeletal osteoma
    3. Extraskeletal / soft-tissue chondroma
    4. Mesenchymal chondrosarcoma
    5. Extraskeletal osteosarcoma
  9. UNCERTAIN DIFFERENTIATION
    1. Intramuscular myxoma
    2. Ossifying fibromyxoid tumor
    3. Synovial sarcoma
    4. Primitive neuroectodermal tumor
    5. Extraskeletal Ewing sarcoma

Most Frequent Benign Soft-tissue Tumors

8 pathologic diagnoses make up 70% of all benign tumors!

  1. Lipoma 16%
  2. Fibrous histiocytoma 13%
  3. Nodular fasciitis 11%
  4. Neurogenic neoplasm 10%
  5. Hemangioma 7%
  6. Fibromatosis 7%
  7. PVNS / giant cell tumor of tendon sheath 4%
  8. Ganglion cyst

Most Frequent Malignant Soft-tissue Tumors

7 pathologic diagnoses make up 80% of all malignant tumors!

  1. Undifferentiated pleomorphic sarcoma (= malignant fibrous histiocytoma) 29%
  2. Liposarcoma 14%
  3. Nonspecific spindle cell sarcoma 12%
  4. Leiomyosarcoma 8%
  5. Malignant peripheral nerve sheath tumor 6%
  6. Dermatofibroma protuberans 6%
  7. Synovial sarcoma 5%

Fat-containing Soft-tissue Masses  !!navigator!!

  1. BENIGN LIPOMATOUS TUMORS
    1. Lipoma
    2. Intra- / intermuscular lipoma
    3. Synovial lipoma
    4. Lipoma arborescens = diffuse synovial lipoma
    5. Neural fibrolipoma = fibrolipomatous tumor of nerve
    6. Macrodystrophia lipomatosa
  2. LIPOMA VARIANTS
    1. Lipoblastoma
    2. Lipomatosis
      1. Madelung disease
      2. Mediastinal lipomatosis
      3. Pancreatic lipomatosis
      4. Pelvic lipomatosis
    3. Hibernoma
  3. MALIGNANT LIPOMATOUS TUMOR
    1. Liposarcoma
  4. OTHER FAT-CONTAINING TUMORS
    1. Hemangioma
    2. Elastofibroma dorsi
  5. LESIONS MIMICKING FAT-CONTAINING TUMORS
    1. Myxoid tumors: intramuscular myxoma, extraskeletal myxoid chondrosarcoma, myxoid malignant fibrous histiocytoma
    2. Neural tumors: neurofibroma, neurilemmoma, malignant schwannoma
      √ 73% have tissue attenuation less than muscle
    3. Hemorrhage

Benign Fibrous Soft-Tissue Tumors  !!navigator!!

So-called Fibrohistiocytic Tumors

  1. Benign fibrous histiocytoma
  2. Diffuse-type giant cell tumor
  3. Malignant fibrous histiocytoma

Benign Myofibroblastic Proliferations

  1. Nodular fasciitis
  2. Proliferative fasciitis / myositis
  3. Fibroma of tendon sheath
  4. Keloid and hypertrophic scar
  5. Elastofibroma

Musculoskeletal Fibromatoses

= wide range of clinicopathologic conditions with benign proliferation of fibrous tissue characterized by infiltrative growth pattern and tendency to recur locally

Superficial Fascial Fibromatoses

  1. Palmar fibromatosis (Dupuytren disease)
  2. Plantar fibromatosis (Ledderhose disease)
  3. Penile fibromatosis (Peyronie disease)
  4. Knuckle pads
    = focal fibrous thickening dorsally at PIP / MCP joint
  5. Juvenile aponeurotic fibroma
  6. Infantile digital fibromatosis

Deep Musculoaponeurotic Fibromatoses

  1. Desmoid-type fibromatosis
  2. Abdominal wall fibromatosis
  3. Mesenteric fibromatosis
  4. Retroperitoneal fibromatosis
  5. Pelvic fibromatosis
  6. Gardner syndrome fibromatosis

Childhood Fibromatosis

  1. Fibromatosis colli
  2. Lipofibromatosis
  3. Calcifying aponeurotic fibroma
  4. Inclusion body fibromatosis
  5. Infantile myofibromatosis
  6. Juvenile aponeurotic fibroma
  7. Infantile digital fibromatosis

Cystlike T2-hyperintense Soft-tissue Lesions on MRI  !!navigator!!

Cause:

  1. true cyst
  2. internal tumor necrosis
  3. high extracellular water content = edema
  4. extracellular matrix of high water + protein content = myxoid stroma
  1. TRULY CYSTIC LESION
    1. Synovial cyst
    2. Ganglion cyst
    3. Distended bursa
    4. Postsurgical collection + hematoma
    5. Skin appendage: eg, epidermal inclusion cyst
    6. Lymphatic malformation
    7. Hydatid cyst
  2. BENIGN SOLID LESION
    1. Myxoma
    2. Peripheral nerve sheath tumor
    3. Vascular lesions: hemangioma, vascular malformation
    4. Glomus tumor
  3. MALIGNANT SOLID LESION
    1. Malignant fibrous histiocytoma = undifferentiated pleomorphic sarcoma
    2. Myxoid sarcoma:
      • myxofibrosarcoma
      • myxoid liposarcoma
      • extraskeletal myxoid chondrosarcoma
    3. Synovial sarcoma
    4. Metastasis

Myxomatous Lesions of Soft Tissue

= tumor with abundance of extracellular mucoid material

√mimicker of cysts ← high water content

  1. BENIGN
    1. Intramuscular myxoma
      • perilesional edema + rim of fat
    2. Synovial cyst
      • communication with joint / tendon sheath
    3. Bursa
    4. Soft-tissue ganglion
      • communication with joint / tendon sheath
    5. Benign peripheral nerve sheath tumor: neurofibroma, schwannoma
      • “entering-and-exiting-nerve” sign
  2. MALIGNANT
    1. Myxoid liposarcoma
      • intralesional fat
    2. Myxoid leiomyosarcoma
    3. Myxoid chondrosarcoma
      • internal chondroid matrix
    4. Ossifying fibromyxoid tumor
      • incomplete peripheral ossification
    5. Myxofibrosarcoma
  3. SYNDROMES
    1. Mazabraud syndrome

Extraskeletal Osseous + Cartilaginous Tumors  !!navigator!!

  1. OSSEOUS SOFT-TISSUE TUMORS
    √ cloudlike “cumulus” type of calcification
    1. Myositis ossificans
    2. Fibrodysplasia ossificans progressiva
    3. Soft-tissue osteoma
    4. Extraskeletal osteosarcoma
    5. Myositis ossificans variants
      1. Panniculitis ossificans
      2. Fasciitis ossificans
      3. Fibroosseous pseudotumor of digits
  2. CARTILAGINOUS SOFT-TISSUE TUMORS
    √ arcs and rings, spicules and floccules of calcification
    1. Synovial osteochondromatosis
    2. Soft-tissue chondroma
    3. Extraskeletal chondrosarcoma

DDx:

  1. Synovial sarcoma
  2. Benign mesenchymoma
    = lipoma with chondroid / osseous metaplasia
  3. Malignant mesenchymoma
    = 2 or more unrelated sarcomatous components
  4. Calcified / ossified tophus of gout
  5. Ossified soft-tissue masses of melorheostosis
  6. Tumoral calcinosis
  7. Pilomatricoma = calcifying epithelioma of Malherbe
    • lesion arises from hair matrix cells with slow growth confined to the subcutaneous tissue of the face, neck, upper extremities
    • central sandlike calcifications (84%)
    • peripheral ossification (20%)

Soft-tissue Uptake of Bone Agents  !!navigator!!

  1. Physiologic
    1. Breast
    2. Kidney: accentuated uptake with dehydration, antineoplastic drugs, gentamicin
    3. Bowel: surgical diversion of urinary tract
  2. Faulty preparation with radiochemical impurity
    1. free pertechnetate (TcO4-)
      • Cause: introduction of air into the reaction vial
      • activity in mouth (saliva), salivary glands, thyroid, stomach (mucus-producing cells), GI tract (direct secretion + intestinal transport from gastric juices), choroid plexus
    2. 99mTc-MDP colloid
      • Cause: excess aluminum ions in generator eluate / patient ingestion of antacids; hydrolysis of stannous chloride to stannous hydroxide, excess hydrolyzed technetium
      • diffuse activity in liver + spleen
  3. Neoplastic condition
    1. benign tumor
      1. Tumoral calcinosis
      2. Myositis ossificans
    2. primary malignant neoplasm
      1. Extraskeletal osteosarcoma / soft-tissue sarcoma: bone forming
      2. Neuroblastoma (35–74%): calcifying tumor
      3. Breast carcinoma
      4. Meningioma
      5. Bronchogenic carcinoma (rare)
      6. Pericardial tumor
    3. metastases with extraosseous activity
      1. to liver: mucinous carcinoma of colon, breast carcinoma, lung cancer, osteosarcoma
        mnemonic: LE COMBO
        • Lung cancer
        • Esophageal carcinoma
        • Colon carcinoma
        • Oat cell carcinoma
        • Melanoma
        • Breast carcinoma
        • Osteogenic sarcoma
      2. to lung: 20–40% of osteosarcomas metastatic to lung demonstrate 99mTc-MDP uptake
      3. Malignant pleural effusion, ascites, pericardial effusion
  4. Inflammation
    1. Inflammatory process (abscess, pyogenic / fungal infection):
      1. adsorption onto calcium deposits
      2. binding to denatured proteins, iron deposits, immature collagen
      3. hyperemia
    2. Crystalline arthropathy (eg, gout)
    3. Dermatomyositis, scleroderma
    4. Radiation: eg, radiation pneumonitis
    5. Necrotizing enterocolitis
    6. Diffuse pericarditis
    7. Bursitis
    8. Pneumonia
  5. Trauma
    1. Healing soft-tissue wounds
    2. Rhabdomyolysis:
      • crush injury, surgical trauma, electrical burns, frostbite, severe exercise, alcohol abuse
    3. Intramuscular injection sites:
      • especially Imferon® (= iron dextran) injections with resultant chemisorption; meperidine
    4. Ischemic bowel infarction (late uptake)
    5. Hematoma: soft tissue, subdural
    6. Heterotopic ossification
    7. Myocardial contusion, defibrillation, unstable angina pectoris
    8. Lymphedema
  6. Metabolic
    1. Hypercalcemia (eg, hyperparathyroidism):
      1. uptake enhanced by alkaline environment in stomach (gastric mucosa), lung (alveolar walls), kidneys (renal tubules)
      2. uptake with severe disease in myocardium, spleen, diaphragm, thyroid, skeletal muscle
    2. Diffuse interstitial pulmonary calcifications: hyperparathyroidism, mitral stenosis
    3. Amyloid deposits
  7. Ischemia / necrosis with dystrophic soft-tissue calcifications
    • Spleen: infarct (sickle cell anemia in 50%), microcalcifications ← lymphoma, thalassemia major, hemosiderosis, glucose-6-phosphate-dehydrogenase deficiency
    • Liver: massive hepatic necrosis
    • Heart: transmural myocardial infarction, valvular calcification, amyloid deposition
    • Muscle: traumatic / ischemic skeletal muscle injury
    • Brain: cerebral infarction (damage of blood-brain barrier)
    • Kidney: nephrocalcinosis
    • Vessels: calcified wall, calcified thrombus

Soft-tissue Calcification  !!navigator!!

Metastatic / Metabolic Calcification

= deposit of calcium salts in normal tissue

  1. as a result of elevation of Ca x P product above 60–70
  2. with normal Ca x P product after renal transplant

Location: lung (alveolar septa, bronchial wall, vessel wall), kidney, gastric mucosa, heart, peripheral vessels

Cause:

  1. Skeletal deossification
    1. 1° HPT
    2. Ectopic HPT production (lung / kidney tumor)
    3. Renal osteodystrophy + 2° HPT
    4. Hypoparathyroidism
    5. Prolonged immobilization
  2. Massive bone destruction
    1. Widespread bone metastases
    2. Plasma cell myeloma
    3. Leukemia
  3. Hypercalcemia
    1. Primary hyperparathyroidism
    2. Hypervitaminosis D
    3. Milk-alkali syndrome
    4. Sarcoidosis
    5. Hydroxyapatite deposition disease
    6. IV administration of calcium salts
  4. Idiopathic hypercalcemia
  5. Hyperuricemia
    1. Tophaceous gout

Dystrophic Calcification

= deposit of calcium salts in tissue damaged by injury / inflammation (with local electrolyte / enzyme alterations) in presence of normal serum Ca + P level

Cause:

  1. Metabolic disorder without hypercalcemia
    1. Renal osteodystrophy with 2° HPT
    2. Hypoparathyroidism
    3. Pseudohypoparathyroidism
    4. Pseudopseudohypoparathyroidism
    5. Gout
    6. Pseudogout = chondrocalcinosis
    7. Ochronosis = alkaptonuria
    8. Diabetes mellitus
  2. Connective tissue disorder
    1. Scleroderma = progressive systemic sclerosis
    2. Dermato- and polymyositis
    3. Systemic lupus erythematosus
    4. Mixed connective tissue disorders
  3. Trauma
    1. Neuropathic calcifications
    2. Frostbite
    3. Myositis ossificans progressiva
  4. Infestation
    1. Cysticercosis
    2. Dracunculosis (guinea worm)
    3. Loiasis
    4. Bancroft filariasis
    5. Hydatid disease
    6. Leprosy
  5. Vascular disease
    1. Atherosclerosis
    2. Media sclerosis (Mönckeberg)

      DDx of Soft-Tissue Calcifications

      Metastatic CalcificationsDystrophic CalcificationsCalcinosis
      Hyperpara-thyroidismSoft-tissue tumor: lipoma, sarcomas (synovial, osteo~, chondro~)Idiopathic tumoral calcinosis
      Hypopara-thyroidismInherited disorder: Ehlers-Danlos, pseudoxanthomaCalcinosis interstitialis universalis
      Milk-alkali syndromeParasitic infectionCalcinosis in SLE, scleroderma, juvenile dermatomyositis
      Excessive vitamin DTophaceous gout
      Sarcoidosis
      Paraneoplastic hypercalcemia
      Destructive bone disease
    3. Venous calcifications
    4. Tissue infarction (eg, myocardial infarction)
  6. Miscellaneous
    1. Ehlers-Danlos syndrome
    2. Pseudoxanthoma elasticum
    3. Werner syndrome = progeria
    4. Calcinosis (circumscripta, universalis, tumoral calcinosis)
  7. Neoplastic disease
    1. Synovial sarcoma
    2. Osteosarcoma
    3. Chondrosarcoma
    4. Necrotic tumor
  8. Degenerative disease
    1. Calcium pyrophosphate deposition disease
    2. Calcific tendonitis (in 3% of adults)
      Location: shoulder >hip >elbow >wrist >knee
    3. Calcific bursitis
  9. Metaplasia
    1. Synovial osteochondromatosis

Generalized Calcinosis

  1. Collagen vascular disorders
    1. Scleroderma
    2. Dermatomyositis
  2. Idiopathic calcinosis universalis

Idiopathic Calcification

  1. Tumoral calcinosis
    • normal calcium + elevated phosphate levels

Interstitial Calcinosis  !!navigator!!

Calcinosis Circumscripta

  • firm white commonly ulcerating dermal papules / plaques / subcutaneous nodules extruding a chalky white material of hydroxyapatite
  1. Acrosclerosis: granular deposits around joints of fingers and toes, fingertips
  2. Scleroderma + CREST syndrome: acrosclerosis and absorption of ends of distal phalanges
  3. Dermatomyositis: extensive subcutaneous deposits
  4. Varicosities: particularly in calf
  5. 1° Hyperparathyroidism: infrequently periarticular calcinosis
  6. Renal osteodystrophy with 2° hyperparathyroidism: extensive vascular deposits even in young individuals
  7. Hypoparathyroidism: occasionally around joints; symmetrical in basal ganglia
  8. Vitamin D intoxication: periarticular in rheumatoid arthritis (puttylike); calcium deposit in tophi

Calcinosis Universalis

= progressive disease of unknown origin

Age: children + young adults

Associated with: poly- and dermatomyositis

  • diffuse plaque- / sheetlike calcium deposits in skin and subcutis; sometimes in tendons + muscles + fascia
  • NO true bone formation

Soft-tissue Ossification  !!navigator!!

= formation of trabecular bone

  1. Myositis ossificans progressiva / circumscripta
  2. Paraosteoarthropathy
  3. Soft-tissue osteosarcoma
  4. Parosteal osteosarcoma
  5. Posttraumatic periostitis = periosteoma
  6. Surgical scar
  7. Severely burned patient

Connective Tissue Disease  !!navigator!!

= CTD = [COLLAGEN VASCULAR DISEASE]

= heterogeneous group of immunologically mediated systemic inflammatory disorders that may affect various organs but share a number of clinical + laboratory features

  • Features:
    1. relatively specific: arthritis, myositis, Raynaud phenomenon with digital ulceration, tethered skin in extremities + trunk, malar rash sparing nasolabial folds, morning stiffness
    2. relatively nonspecific: polyarthralgias (most common initial symptom), myalgias, mottling of extremities, muscle weakness + tenderness
  • Laboratory findings:
    1. relatively specific: ANA in peripheral rim / nucleolar pattern, anti-DNA, elevated muscle enzyme
    2. relatively nonspecific: ANA in homogeneous pattern, anti-single-stranded DNA, positive rheumatoid factor

Types and most distinctive features:

  1. Rheumatoid arthritis positive rheumatoid factor, prominent morning stiffness, symmetric erosive arthritis
  2. Systemic lupus erythematosus malar rash, photosensitivity, serositis, renal disorders with hemolytic anemia, leukopenia, lymphopenia, thrombocytopenia, positive ANA
  3. Sjögren syndrome dry eyes + mouth, abnormal Schirmer test
  4. Progressive systemic sclerosis
  5. Raynaud phenomenon, skin thickening of distal extremities proceeding to include proximal extremities + chest + abdomen, positive ANA in a nucleolar pattern
  6. Polymyositis, dermatomyositis heliotrope rash over eyes, proximal muscle weakness, elevated muscle enzymes, inflammation at muscle biopsy
  7. Mixed connective tissue disease

Thoracic imaging pattern: (see table)

Muscle  !!navigator!!

MR signal intensity of normal muscle:

  • higher than water + lower than fat on T1WI
  • much lower than water + fat on T2WI

Intramuscular Mass

  1. NEOPLASM
  2. INFECTION / INFLAMMATION
    1. Intramuscular abscess
    2. Focal myositis = benign inflammatory pseudotumor
    3. Necrotizing fasciitis
    4. Sarcoidosis
      • nodules with central star-shaped area of fibrosis surrounded by granuloma
  3. MYONECROSIS
    1. Sickle cell crisis
    2. Poorly controlled diabetes
    3. Compartment syndrome
    4. Crush injury
    5. Severe ischemia
    6. Intraarterial chemotherapy
    7. Rhabdomyolysis = severe muscle injury with loss of integrity of muscle cell membranes
      • Cause: trauma, severe exercise, ischemia, burn, toxin, IV heparin therapy, autoimmune inflammation
      • Cx: renal damage from myoglobulinemia, tetany, compartment syndrome
  4. TRAUMA
    1. Intramuscular hematoma (eg, severe muscle strain, laceration, contusion, spontaneous)
    2. Myositis ossificans traumatica

Frequency of Thoracic CT Findings of Connective Tissue Disease

Mixed Connective Tissue DiseaseDermatomyositis PolymyositisProgressive Systemic SclerosisJuvenile Idiopathic ArthritisSystemic Lupus Erythematosus (SLE)
Ground-glass opacity+++++++++++++++
Septal thickening++++++++++
Honeycombing++++++++++
Consolidation++++++++++
Crazy paving————++
Pulmonary nodules———++—
Pleural / pericardial effusions++—+++++++++
Progressive ↓ of lung volume+++++++
Pulmonary embolism————+
MPA dilatation++++++

Pulmonary Manifestations of Collagen Vascular Disease

TypeUIPNSIPCOPLIPDADHemorrhageAirway disease
Rheumatoid arthritis+++++++++–+++
Progressive systemic sclerosis+++++–+––
Dermato- / polymyositis+++++++–++––
Sjögren syndrome++++–+++_+
Mixed connective tissue disease++++––––
Systemic lupus erythematosus++++++++++–

COP = Crytpogenic Organizing Pneumonia, DAD = Diffuse Alveolar Damage, LIP = Lymphocytic Interstitial Pneumonia, NSIP = Nonspecific Interstitial Pneumonia, UIP = Usual Interstitial Pneumonia

Thoracic Manifestations of Collagen Vascular Disease

Ankylosing SpondylitisDermatomyositis PolymyositisProgressive Systemic SclerosisRheumatoid ArthritisSjögren SyndromeSystemic Lupus Erythematosus (SLE)
Pulmonary fibrosisoccasionalcommonfrequentfrequentoccasionaloccasional
Pleural disease———frequent—frequent
Diaphragm weakness—frequent———frequent
Aspiration pneumonia—frequentfrequent———
Bronchiectasis———occasionalcommon—
Apical fibrosisfrequent—————
Bronchiolitis obliterans———common——
BOOP—common—common——

Muscle Edema

√muscle hyperintensity on STIR images

  1. INFLAMMATION
    1. Dermatomyositis
    2. Polymyositis
    3. Radiation therapy: straight sharp margins, involves muscle + subcutaneous fat
    4. Early stage of myositis ossificans
  2. CELLULAR INFILTRATE
    1. Lymphoma
  3. INFECTION
    1. Bacterial / infectious myositis
      1. direct extension from adjacent infection (eg, osteomyelitis, subcutaneous abscess)
      2. hematogenous
    2. Inclusion body myositis (probably due to paramyxovirus infection) resembling polymyositis
  4. RHABDOMYOLYSIS
    1. Sport / electric injury
    2. Diabetic muscular infarction
    3. Focal nodular myositis
    4. Metabolic myopathy: eg, phosphofructokinase deficiency, hypokalemia, alcohol overdose
    5. Viral myositis
  5. TRAUMA
    1. Subacute muscle denervation
      Time of onset: 2–4 weeks after denervation
      Mechanism:
      • spinal cord injury, poliomyelitis, peripheral nerve injury / compression (ganglion cyst, bone spur), Graves disease, neuritis
    2. Muscle contusion (from direct blow)
    3. Muscle strain (= injury at musculotendinous junction from overly forceful muscle contraction)
      Predilection for: hamstring, gastrocnemius m., biceps brachii m.)
    4. Delayed-onset muscle soreness
      = overuse injury becoming symptomatic hours / days after overuse episode
    5. Compartment syndrome
      = increased pressure within indistensible space of confining fascia leading to venous occlusion, muscle + nerve ischemia, arterial occlusion, tissue necrosis
      Cause: trauma, burns, heavy exercise, extrinsic pressure, intramuscular hemorrhage
      • severe pain
      • dysfunction of sensory + motor nerves passing through affected compartment

      Rx: urgent fasciotomy
    6. Sickle cell crisis

Fatty Infiltration of Muscle

  1. Chronic stage of muscle denervation (eg, poliomyelitis, stroke, peripheral nerve injury)
  2. Chronic disuse (eg, chronic tendon tear, severe osteoarthritis)
  3. Late stage of severe muscle injury
  4. Long-term high-dose corticosteroid medication affecting truncal muscles

 Outline