Lower limb necrotizing fasciitis

By Ma Wai Kit, MRCS, Lee Fung Yee Janet, FRCS Ed, Wong Kwok Chuen, FRCS Ed, Yiu Ying Chang Raymond, FRCS Ed, Li Chak Man Jimmy, FRACS
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Lower limb necrotizing fasciitis

Findings

Contrast-enhanced CT showed rim-enhancing loculated collections with air pockets in the left piriformis and glutei (Figure 1) extending down to the vastus lateralis muscles (Figure 2). There was intrapelvic extension via the involved left piriformis, which was inseparable from the recurrent rectal tumor (Figure 1). A segment of thickened small bowel was intimately related to the recurrent tumor (Figure3).

CLINICAL FINDINGS

Based on the CT findings, emergency surgery was scheduled. During exploration, a large abscess was noted over the gluteal region extending down to the lateral aspect of the thigh. Incision and drainage of the abscess with debridement of the necrotic tissues was performed. The necrotic tissue grew Escherichia coli and Klebsiella sp. However, his sepsis was not under control, and another surgical debridement was performed 48 hours later (Figure 4). Extensive muscle necrosis was noticed, which involved the piriformis, gluteal muscles, short external rotator muscles, and the quadriceps. Moreover, feculent material was draining through the medial aspect of the piriformis (Figure 4). In view of the extensive muscle involvement and overall poor prognosis, the patient was put on supportive care, and he died 3 days later.

Discussion

Necrotizing fasciitis is an uncommon but serious soft tissue infection that is associated with extensive local tissue destruction, systemic toxicity, and a fulminant clinical course. More than 500 cases have been reported in the literature.1 Despite surgical advances and the introduction of potent antimicrobial agents, mortality rates of 30% to 60% have been reported.2 The time course and clinical presentation of necrotizing fasciitis varies. It can progress from days to weeks with nonspecific systemic complaints or vague localizing symptoms. The overlying skin appearance is often subtle in the early stage, with erythema that may be mistaken as cellulitis. However, vesicles, bullae, necrosis, or crepitus should prompt the diagnosis of necrotizing soft tissue infection.3 Severe pain out of proportion to physical findings is an important clue for distinguishing simple cellulitis from deep-seated soft tissue infection. Lack of natural boundaries along the fascial planes explains the rapidity of the spread of infection and the deterioration in clinical condition.

Sometimes, imaging studies including plain radiograph, computed tomography (CT), or magnetic resonance imaging (MRI) may facilitate the diagnosis of this surgical emergency. Plain radiographs are insensitive in the early stage of the disease, as findings such as an increase in soft tissue thickness and opacity4 are similar to those of cellulitis. The presence of soft tissue gas is characteristic of necrotizing soft tissue infection, though this is not a universal finding.3,5,6 CT is more sensitive than plain radiographs in detecting soft tissue gas.6 The presence of soft tissue gas dissecting along fascial planes is suggestive of necrotizing fasciitis.7In addition, CT can detect thickening and enhancement offascial layers with or without fluid collection.8 In our case, CT was a useful tool to make the diagnosis, to assess the extent of the soft tissue infection and to ascertain the infectious source by exhibiting the intrapelvic extension of inflammatory changes via the piriformis muscle. For patients with renal impairment at the time of presentation, contrast-enhanced CT may not be advisable and MR canbe an alternative diagnostic adjunct. In general, the presence of fascial fluid can be better appreciated on fat-suppressed T2-weighted images than on fat-suppressed gadolinium-enhanced T1-weighted images.9 However, the sensitivity of MR exceeds its specificity, as both inflammatory edema and liquefactive tissue necrosis produce similar MR appearance and, therefore, the extent of infection can be overestimated.4,9 In practice, CT or MR is the best radiological tool of choice to be used in suspected cases of necrotizing fasciitis to expedite the diagnosis. However, surgical treatment should never be delayed by radiological imaging.

Necrotizing fasciitis is a rare complication associated with colorectal malignancy. There are only few reported cases in the English language literature to date.10-16 Almost all of these were related to bowel perforation. They may present as Fournier's gangrene (necrotizing perineal infection 10, 12-14 psoas abscess,11or direct tumor invasion into the abdominal wall.15 In this case, tumor perforation should be the underlying cause for necrotizing fasciitis. The presence of bowel contents draining from the medial aspect of the left piriformis in this patient signified direct communication between the thigh muscles and the recurrent rectal anastomosis tumor. This might be the result of multiple courses of chemotherapy, which led to tumor necrosis and subsequent bowel perforation. In view of the significant amount of feculent material draining from the rectum through the greater sciatic notch in the presence of fecal diversion (colostomy), we suspected that there might be an underlying fistula between the adherent small bowel loop and the recurrent rectal tumor either as a result of previous radiotherapy or direct tumor invasion. We believe that the progression of sepsis after the first debridement could be a combined result of inadequate removal of necrotic tissue and continued spillage of gastrointestinal contents through the greater sciatic notch.


Conclusion

 Necrotizing fasciitis is a rapidly progressing soft tissue infection. The clinical outcome relies on the clinician’s acumen and index of suspicion. Cross-sectional imaging techniques can be used to hasten the diagnosis. Prompt diagnosis followed by early antimicrobial therapy andadequate surgical debridement are the key factors in minimizing morbidities and mortality of necrotizing fasciitis.


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Lower limb necrotizing fasciitis.  Appl Radiol. 

November 05, 2008



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