Fulminant necrotising fasciitis from subclinical appendicitis

Clinical History

84-year-old man presented with vague right hip pain following a fall. Initial hip radiographs were normal, and he was discharged with a provisional diagnosis of soft tissue injury.

He re-presented 24 hours later with severe hypotension and tachycardia, CRP of 376 and normal WCC. He was apyrexial.

Imaging Findings

Initial radiographs (Fig. 1) were normal. The patient was noted to have a soft, non-tender abdomen, with full range of hip movement.

Pelvic and right femur radiographs acquired 1 day later (Fig. 2) demonstrate lucencies along the muscular fascia planes corresponding to gas locules.

Emergency exploration of the right thigh with washout and debridement of necrotic tissues was performed with the surgeon noting that the infection was tracking from the pelvic compartment.

In Fig. 3 and 4, an appendiceal abscess is present in the right iliac fossa with an appendicolith within it. The abscess is in contact with the right iliacus and psoas muscle. Inflammation and gas locules are noted around the right iliopsoas muscles, extending into the right hip and thigh musculature, tracking along the muscular fascial planes.

CT-guided drain insertion was performed with a Merit One stop centesis catheter (Fig. 5).

Discussion

Necrotising fasciitis is an uncommon, life-threatening musculoskeletal soft tissue infection. It follows an aggressive and rapidly progressive course, with the infection spreading along the deep muscular fascia planes [1]. Aetiological organisms are typically polymicrobial incorporating aerobic and anaerobic organisms ranging from Staphyloccocus and Streptococcus to Clostridium and Klebsiella [2, 3, 4]. Predisposing risk factors include intravenous drug and alcohol abuse, post-surgical wounds, diabetes, obesity, peripheral vascular disease and immunocompromised patients [1, 5]. Rarely, intra-abdominal causes like diverticulitis or in this case, a subclinical appendiceal abscess is the source.

Early diagnosis is essential but this is often hindered by non-specific signs and symptoms. A high index of clinical suspicion is required but radiology can aid in providing a rapid diagnosis.

Initial plain radiographs of the affected body part are frequently normal. As the infection progresses, locules of gas may be seen within the deep soft tissues orientated along the fascial planes [6]. Overlying soft tissue thickening can be present, though this can mimic cellulitis.

Ultrasound is useful particularly in the paediatric population [5]. The key sonographic findings are that of fascial thickening, interfascial fluid collections and subcutaneous oedema, with or without the presence of gas. Hyperaemia [7] and small vessel thrombosis [8] may also be identified.

Cross-sectional imaging can offer information in regards to the extent, and in this case, a cause of the infection. The characteristic CT findings are that of gas within the deep soft tissues along the muscle fasciae, accompanied with inflammatory stranding, asymmetrical fascial thickening and enhancement, fluid collections and abscesses [1, 5]. Associated changes like reactive lymphadenopathy and subcutaneous oedema can help localisation. CT imaging was required in this patient to determine the intra-abdominal cause of infection as well as providing an interval therapeutic procedure via CT-guided drainage of the appendiceal abscess.

MRI findings can demonstrate high T2w inflammatory signal change within the deep tissue, best appreciated on fat-supressed sequences [5]. Altered and heterogeneous signal intensity of the muscle with increased T1w signal would indicate intramuscular necrosis and haemorrhage. Post-gadolinium sequences often demonstrates soft tissue inflammatory enhancement. However, this is not required for diagnosis as necrotic tissues, fluid pockets and abscesses may demonstrate no enhancement [9].

When the diagnosis is made, urgent surgical intervention with fasciotomy and debridement of necrotic tissues are typically required. Broad spectrum antibiotic cover is also initiated until cultures yield an aetiological organism [1, 5].

Differential Diagnosis List

Final Diagnosis

Fulminant necrotising fasciitis from subclinical appendiceal abscess.

URL:	https://www.eurorad.org/case/12133
DOI:	10.1594/EURORAD/CASE.12133
ISSN:	1563-4086