We retrospectively reviewed 49 patients with bowel strangulation proved by surgical operation (April, 2007-October, 2014 ).  We estimated clinical, CT, and surgical findings and compared those between stages, which were diagnosed according to CT findings. 

1) Evaluated factors include;

• Time from onset to CT scan (Onset-to-scan time: OST)

• Time from CT scan to operation(Scan-to-operation time: SOT)

• Time from onset to operation time (Onset-to-operation time: OOT)

• Clinical symptoms

• Presence of peritoneal irritation

• LDH(Lactate dehydrogenase)

• CPK(Creatine phosphokinase)

• CT findings

• Bowel resection +/-

2) CT staging for bowel strangulation is as follows (Fig.1-5);

Stage I: Because of low pressure of the flow, the venous system is affected earlier than the arterial system, which results in bowel and mesenteric edema in the closed loop. On stage I arterial pressure is high enough to feed the loop through the “strangulation hilum”. 

Stage II: As intrinsic pressure of the closed loop gets higher with progressive edema or the “strangulation hilum” gets tighter, arterial supply gets slower and decreased. On stage II the loop is going to be ischemic. 

Stage III: When the intrinsic pressure of the closed loop gets high enough or the “hilum” gets tight enough, the arterial flow cannot go through the “hilum” into the closed loop. On stage III the loop is going to be necrotic. 

Stage IV: Bowel necrosis gets evident on stage IV. Hyperdense appearance of the bowel wall suggesting hemorrhagic necrosis, bowel and mesenteric pneumatosis, free air due to perforation of the necrotic bowel can be noted even on non-enhanced CT.

Fig. 1: Schematic illustration of the stages of bowel strangulation.
References: Department of Emergency and Critical Care Medicine, St. Marianna University School of Medicine - Kawasaki/JP

Fig. 2: Stage I: Bowel and mesenteric edema due to venous congestion. On stage I territorial bowel and mesenteric edema in the closed loop is the only finding on CT. Well enhanced thickened bowel wall can be noted on both arterial and equilibrium phases on dynamic CT scan. Prolonged enhancement might be observed if delayed phase scan is done because of venous congestion. CT images show edematous mesentery (arrowheads) with well enhanced bowel wall in the closed loop on both arterial and equilibrium phases.
References: Department of Emergency and Critical Care Medicine, St. Marianna University School of Medicine - Kawasaki/JP

Fig. 3: Stage II: Arterial insufficiency. On stage II poor or no enhancement of all or a part of the closed loop can be noted on arterial phase of the dynamic scan. On equilibrium phase the loop should be enhanced. Bowel and mesenteric edema is also noted. It is impossible to differentiate stage II from stage I without arterial phase because the loop can be well enhanced on equilibrium phase. It is very important to identify this stage because ischemic process has already started, and early surgical intervention should be considered to save affected bowel loop before it gets necrotic. CT images show poor enhancement of the closed loop on arterial phase and the loop is well enhanced on equilibrium phase.
References: Department of Emergency and Critical Care Medicine, St. Marianna University School of Medicine - Kawasaki/JP

Fig. 4: Stage III: Severe bowel and mesenteric ischemia. On stage III very poor or no enhancement of all or a part of the closed loop can be noted on both arterial and equilibrium phases of dynamic scan. Because of lack of blood supply the affected loop is thought to be getting necrotic very soon. If non- or very-poorly enhanced bowel is just a part of the closed loop immediate surgical intervention may save the rest or most of the closed loop. CT images show no enhancement of the closed loop on both phases of dynaminc CT scan.
References: Department of Emergency and Critical Care Medicine, St. Marianna University School of Medicine - Kawasaki/JP

Fig. 5: Stage IV: Bowel and mesenteric necrosis. On stage IV one or some of the evidences of the bowel necrosis can be noted even on non-enhanced CT. Evidences include hyperdense appearance of the bowel wall suggesting hemorrhagic necrosis, bowel and mesenteric pneumatosis, free air due to perforation of the necrotic bowel. The ischemic/necrotic status of the bowel loop is basically the same as stage III if the whole closed loop is affected; stage III and IV are overlapped. Non-enhanced CT images show hyperdense appearance of the bowel wall (arrowheads) in the affected loop, suggesting hemorrhagic necrosis. Hyperdense appearance is more evident on images in narrow window settings. It is hard to identify the hyperdense necrotic loop on enhanced CT because of its hyperdenseness before enhancement.
References: Department of Emergency and Critical Care Medicine, St. Marianna University School of Medicine - Kawasaki/JP

CT findings on each stage of bowel strangulation on dynamic CT are summarized below (Table 1). On all stages evidence of closed loop and bowel and mesenteric edema which initially starts with venous congestion can be noted. As stage gets advanced evidences of decreasing blood supply and progressive ischemia/necrosis can be noted. 

Table 1: CT findings on each stage of bowel strangulation.
References: Department of Emergency and Critical Care Medicine, St. Marianna University School of Medicine - Kawasaki/JP

3) CT images were evaluated and staging was done for all cases by two board-certified radiologists.