Skeletal Muscle - Edema
comment:Edema in skeletal muscle, as in other tissues, is histologically identified by the expansion of interstitial tissue by amorphous to fibrillar, clear to pale eosinophilic material that separates and surrounds individual myofibers ( Figure 1 , Figure 2 , Figure 3 , and Figure 4 ). It is important to distinguish interstitial spaces that are expanded due to edema from those created in normal tissue as a result of fixation or sectioning artifact ( Figure 5 ). Separation as a result of artifact lacks the presence of pale eosinophilic fibrillar material between muscle fibers and bundles.
While edema can occur as a primary lesion ( Figure 1 , Figure 2 , Figure 3 , and Figure 4 ), it most commonly occurs secondary to necrosis and inflammation; regions of hemorrhage are often accompanied by edema. Intramuscular edema can be seen in association with autoimmune conditions, such as polymyositis and dermatomyositis; mild injuries; infectious myositis; subacute denervation; compartment syndrome; and rhabdomyolysis; it can also be seen as a transient, physiologic finding during and briefly following muscle exercise.
recommendation:When intramuscular edema is the sole or primary lesion, it should be diagnosed and graded. In instances where intramuscular edema is a secondary lesion (e.g., to inflammation), it should not be recorded separately unless warranted by severity but should be described within the pathology narrative.
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