Teaching Case

40-year-old female patient with acute regional forearm pain and flexor compartment swelling following the second unit of a blood transfusion (transfusion was immediately stopped). An emergency fasciotomy was then performed. While the swelling resolved, the patient continued to lose function corresponding to all flexor and some extensor arm muscles.

Axial T1 weighted image shows (Fig. 1) evidence of a fasciotomy and loss of fat planes but no appreciable intrinsic muscle abnormality while the T2 weighted fat saturated image (Fig. 2) shows widespread oedema represented by extensive high signal involving almost all of the flexor compartmental muscles as well as some of the muscles in the extensor compartment and surrounding soft tissues. On T1 post contrast fat suppressed images (Fig. 3, 4), there is widespread non enhancement involving almost all of the flexor compartment musculature and well as some of the extensor compartment musculature. Flow void as well as contrast enhancement is observed within the surrounding subcutaneous veins indicating satisfactory venous drainage (Fig. 4) and therefore implying some intact arterial supply. There were no clinical or biochemical features to suggest any infection making intramuscular abscesses unlikely. Therefore a regional non-infective myonecrosis was considered the most likely diagnosis.

Myonecrosis is a term referring to death of muscle and can occur in a number of situations. On MRI, it is characterised by non enhancement of muscle. Perifascial fluid collections, subcutaneous oedema, peripheral enhancement of muscle following contrast have also been described as adjunctive MRI findings [1].

Among the many causes of myonecrosis include diabetic myonecrosis [2, 3, 5], chronic graft versus host disease (GVHD) [3], various drug overdoses (e.g. heroin, cocaine, barbiturates [4]), sickle cell crises, crush injuries, severe ischaemia, intra-arterial chemotherapy and various conditions causing rhabdomyolysis.

Focal (or regional) myonecrosis has been described following compartmental syndrome but usually occurs before a fasciotomy or when a fasciotomy has been delayed [3].

An unusual feature in this case is that the myonecrosis extends beyond one compartment (i.e. involves both the flexor and extensor compartments) which implies that a pure compartment syndrome could not have been the sole causative factor.

Rhambdomyolysis has previously been reported to occur with heparin [3] which may have been a possible contributor in this case especially considering the patient receiving a blood transfusion immediately prior to the event, although this is not proven in this case.