Post-surgery necrotising fasciitis invading the rectus abdominis muscle

Clinical History

One day after an anterior rectum surgical resection with a termino-terminal anastomis, for a rectal neoplasm, the patient showed sudden pain in the soft tissues of right flank and fever. Clinical examination showed a swollen and hot skin and "crackling snow crepitus". Patient underwent Thorax-Abdomen Contrast-enhanced CT (CECT).

Imaging Findings

Scans showed the outcomes of the surgery and two drainage pipes were present, one in the right pelvis, one in the left flank (Fig. 1).
Close to the right drainage access a suspected infection characterised by huge air-densities, collections and oedema extending along the soft tissues as right subcutaneous fat, parietal abdominal muscles and subcutaneal fascia were present (Fig. 2). Scout of subcutaneous emphysema which extends up to the supracalvicular region was present (Fig. 3).Solution of continuity, 1.5 cm, of the rectus abdominis muscles was observed, the mesenterial fat tissues appeared hyperdense, small amount of pleural and pericardial effusion were seen (Fig. 4). CT findings, due to the invasion of the fascia, were suggestive for Necrotising Fasciitis (NF) starting from the right drainage pipe. Patient immediately underwent surgical debridement of the tissue involved and suture of the rectum abdominis muscles was made. Antibiotics were administrated and the patient survived.

Discussion

NF is a rare, life-threatening, soft-tissue infection characterised by rapidly spreading inflammation and necrosis of the skin involving the subcutaneous tissues and fascia due to the spreading of bacteria among and inside the skin surface [1]. The disease may occur if the right set of conditions is present, these include an opening in the skin that allows bacteria to enter the body, as in our case where the infection spread up to the access of the right drainage pipe. Symptoms appear usually within 24 hours of a minor injury, and include: pain in the general area of the injury and worsening over time and flu-like symptoms such as nausea, fever, diarrhoea, dizziness and general malaise [2]. CT imaging is needed to distinguish NF from other infection of the soft tissues: cellulitis, non-necrotising fascitis, soft tissues abscess and infectious myositis. In cellulitis there is no involvement of the fascia while in NF it is a constant finding. Subcutaneous gas is only present in NF. Others CT findings in NF include thickening of the affected fascia, fluid collections along the fascia sheats, and oedema of the muscular septa. After contrast injection there is no demonstrable enhancement of the fascia in the NF, a finding that confirms the presence of necrosis and helps to distinguish non-necrotising fasciitis from necrotising fasciitis. Soft tissue abscess presents as a well-demarcated fluid collection with a pheripheral pseudocapsule ring enhancement typical of the abscess. In the infectious myosity muscles appears enlarged with a decreased attenuation, and the subcutaneous tissue is not involved [3, 4]. MRI imaging could be useful to evaluate the precise extent of the infection and to distinguish mild fascial or muscle involvement. [5] Nuclear imaging studies (99mTC-Phosphate Complex and 67Ga) are useful in those cases where a complication of oshteomyelitis is suspected [6, 7]. Treatment consists in anitbiotic therapy, surgical debridement of the involved tissue, and hyperbaric oxygen in selected cases. Prognosis depends on the time the diagnosis is made and on the type of bacteria involved. Surgical debridement of the dead tissues is the main goal of the therapy [8]. CT plays a fundamental role in distinguishing NF from other soft tissues infection and can stage the spread of the disease.

Differential Diagnosis List

Final Diagnosis

Post-surgery necrotising fasciitis invading the rectus abdominis muscles.

URL:	https://www.eurorad.org/case/10986
DOI:	10.1594/EURORAD/CASE.10986
ISSN:	1563-4086