|ECR 2019 / C-2194|
|Retroperitoneal necroses: a challenge for the radiologist.|
Findings and procedure details
Retroperitoneal diseases are typically an emergency condition that require an early diagnosis to ensure an optimal management. As clinical symptoms are frequently vague and mild, and local examination is not easily accessible by clinicians, an early diagnosis may be hard.
Affected patients may show critical predisposing factors (e.g. diabetes, immunocompromised status, chronic renal failure) that decrease the prognosis in terms of overall survival.
Retroperitoneal diseases may manifest in form of fluid effusions, inflammatory collections and pneumoretroperitoneum; in particular, retroperitoneal necroses can be life-threatening complications of several predisposing pathologies frequently associated with free gas collections. A correct identification of their etiology is challenging both because the pneumoretroperitoneum is not specific and because the differential diagnosis is broad (Table 1).
A summary of necrotic/gas forming pathologies and their differential diagnosis follows.
Necrotizing fasciitis (NF)
Rare infection of the soft tissues characterized by the systemic diffusion and progressive necrosis of the muscle fascia and the adjacent soft tissue. It is associated with high mortality rates (up to 40%). Usually, polymicrobial infection (Type 1) occurs in patients with diabetes and peripheral vascular diseases and it is more aggressive than monomicrobial (type 2).
Typical locations are abdominal wall, extremities and perineum. Infection finds a breeding ground along the muscle fascia because it is poorly vascularized.
Perianal abscesses, perforated diverticulitis, gangrenous appendicitis, emphysematous pyelonephritis are only some of the etiological causes.
Common risk factors are: diabetes, immunosuppression and vascular diseases. Trauma, mucosal damage, recent surgical procedure and alcoholism are more uncommon. Pregnancy and gynaecologic procedures can predispose to fasciitis in women.
Therapy with antibiotics and surgical debridement may reduce the aggressiveness of the necrotic process.
The radiologist has an important role in the evaluation of the disease because of clinical status, physical examination and laboratory findings may be inconclusive.
Nevertheless, the gold standard in the diagnosis of NF is the surgical biopsy.
The infection is usually sustained by Streptococci, usually as complication of gangrenous and gas-forming pathologies of abdomen.
- Free gas between fasciae and in the abdominal wall. However, the lack of gas does not exclude the presence of the necrotizing form of the fasciitis.
- Presence of vascular thrombosis increases the suspicion of NF.
- Other typical findings are the asymmetrical fascial thickening with enhancement, muscular edema, fluid collections, multifocal abscesses and fat stranding.
Fournier gangrene is the necrotizing fasciitis of the perineum (Fig. 11) . Named after its discoverer, it was first described in 1883.
It is a rare, life-threatening disease that occurs most frequently in middle-age men, secondary to local mixed aerobic and anaerobic infection, diverticulitis, malignancies or iatrogenic.
Given that the emergency status of these patients, radiologist is often necessary to support clinicians in the diagnosis.
- Asymmetric fascial thickening;
- Fluid and purulent collections;
- Free gas has an inter-fascial distribution and can extend to scrotum, inguinal regions, thighs (Fig. 12) and abdominal retroperitoneum.
CT finding of pneumoretroperitoneum invites the radiologist to discriminate between its potential causes.
Emphysematous pancreatitis and pyelonephritis, perforated diverticulitis, gangrenous appendicitis and perineal infections may be either the cause of retroperitoneal NF or a serious problem of differential diagnosis.
Emphysematous pancreatitis (Fig. 13)
Emphysematous pyelonephritis (Fig. 14)
Rare complication of pyelonephritis, due to the infection of the necrotic renal tissue.
Patients are frequently elderly, diabetics with or without an excretory system obstructive disease.
The diagnosis may be delayed as a result of non-specific clinical symptoms, resulting in increased mortality of these patients.
When pyelonephritis is suspected, CT imaging is recommended because it allows the identification of typical findings of the disease (e.g. enlarged kidney, necrotic parenchyma, free air bubbles and/or abscesses); moreover, radiological examination may evaluate the extension of the disease that correlates with the prognosis.
Prompt antibiotic therapy and drainage of the collections reduce the mortality; surgical nephrectomy is limited to emergency cases.
Perianal abscesses (Fig. 15)
Perianal abscesses are inflammatory collections in the perianal region; are usually associated with the presence of perianal fistulae. Patients typically report perianal pain. Drainage of the collection is the main treatment.
Although uncommon, perianal abscesses may complicate, creating the conditions for necrotizing fasciitis and increased risk of mortality.
CT imaging has a limited role in the diagnosis of fistulae, which are properly assessed by MRI. Sensitivity of CT increase in case of complications as abscesses and pneumoretroperitoneum.
Gangrenous appendicitis (Fig. 16)
Appendicitis is one of the most common causes of acute abdomen.
Retrocecal position of appendix is a common anatomical variant, for which it comes into close contact with the retroperitoneum and the psoas sheath.
Although retroperitoneal perforation is uncommon, it is important for the radiologist to consider it in the differential diagnosis because of its complications.
- Presence of appendicolith is usually seen in appendicitis
- Thickening enhancing wall after medium contrast
- Lumen diameter > 6 mm
- Periappendiceal fat stranding
- Enlarged nodes
- Fluid effusion
Retroperitoneal abscesses and pneumoretroperitoneum are serious complications in case of perforation.
Abdominal wall sepsis and thigh emphysema can evolve into a fulminant form.
Diverticulitis (Fig. 17)
Inflammation of bowel wall diverticulosis is a common condition in patients presenting in emergency rooms with acute abdomen (10 %–25 %).
In more than 75% of diverticulosis, the perforation opens in the retroperitoneal space.
Since the involvement of this space is often clinically silent, CT examination has an important role in the detection both of the typical sign of diverticulitis and of its complication, such as abscesses, phlegmons, extravasation of fluid and air.
Small size perforations can be appropriately controlled with medical treatment, while in case of severe complications aggressive surgical management becomes necessary, following the Hinchey classification.
- Wall thickening
- Enhancement of colonic wall
- Pericolonic fat stranding
Complications may be abscesses, phlegmons and extravasation of fluid.
Poor treatment response may result in rapid evolution to NF.
Other causes of pneumoretroperitoneum are following described.
Hollow viscus perforation
CT has higher sensitivity than X-ray in detecting free air collections; usually, the site of perforation may be suspected even if not visible, as extraluminal air tends to collect in the proximity of the wall defect.
Peptic ulcer disease (Fig. 18) affects 6% of population and may become an emergency with rapid onset of peritonism and shock. It is caused by chronic stimulation of gastric acid on the mucous membrane or poor balance between factors stimulating gastric secretion and protective factors. Helicobacter pylori is still the leading predisposing factor of duodenal ulceration. Post-prandial burning pain is the main symptom.
Except for the first portion, the duodenum has a retroperitoneal position. Peptic ulcer usually affects the duodenal bulb, whereas in case of blunt trauma the descending and horizontal segments are more frequently affected.
- focal breach of the wall
- Free abundant extraluminal air, usually, close to the perforation and in the APS.
- Fat stranding and fluid effusion are other associated signs and relate to the inflammatory process.
Complication of endoscopic or intraoperative procedures in patients with advanced age or with other concomitant pathology.
- Retroperitoneal perforation is an uncommon complication of ERCP (0.5%-2% of cases), due to the involvement of the bile duct or the periampullary region. Usually, a perforation at this level leads to a diffusion of large amounts of air, even if these amounts do not correlate with the severity of the damage.
Air distributes to the APS, and from here it may spread over all the retroperitoneal spaces and even the mediastinum and subcutaneous tissues.
The presence of extraluminal air in close proximity to duodenum or hepatoduodenal ligament in the immediate post-operative time has to be considered a consequence of the endoscopic procedure.
- Colon perforation after diagnostic colonoscopy has an incidence of 0.2-0.5%, which approaches 2% in case of therapeutic aim.
Perforation can be secondary to barotrauma for excessive distension of the lumen, to manipulation of the endoscope or to use of therapeutic procedures (dilation or electrocoagulation).
Most frequent locations are sigmoid and cecum.
Surgical treatment is often required in presence of pneumoretroperitoneum.
Blunt trauma (Fig. 21)
Malignancies (Fig. 22)
Colorectal carcinoma is one of the most frequent neoplasm worldwide with more than 1 million people being affected each year. Recto-sigmoid tract and the right colon are currently the most affected locations.
Perforation of colorectal carcinoma accounts for 20% of the patients that present to the emergency departments.
The perforation involves the intestinal tract either close to the tumor site or proximal to it as a result of the ileum.
- Stenosing solid tissue with increasing attenuation with medium contrast
- Regional enlarged nodes.
- Perforation can be suspected if wall ulceration, extraluminal abscesses and air collections are visible.
Patients are generally older and usually, suffer from severe atherosclerotic disease and cardiopathy. Poor blood flow causes the necrosis and the perforation of the bowel wall.
- Wall thickening with submucosal edema (target sign);
- Pneumatosis intestinalis
- Portal venous gas;
- Reduced or absent opacification of the vessels during Angio-CT examination
- Pericolic fat stranding.
- The breach of the wall, inflammatory collections and extraluminal fluid and gas may all be visible in case of perforation.
Reduced perfusion of the bowel can be due by ischemia of superior and inferior mesenteric artery. Systemic reduce blood flow affects preferentially the watershed areas (splenic flexure and recto-sigmoid junction).
Rectum is rarely involved in ischemic processes because the three rectal arteries ensure the perfusion of the organ.
Some cases are reported in literature in patients with atherosclerotic disease, cardiomyopathy, vasculitis and after surgical treatment of iliac vessels.
Surgical aggressive management is required in case of severe ischemic disease with gangrene.
Bladder perforation (Fig. 25)
Bladder can perforate after trauma. More rarely, it perforates spontaneously.
Retroperitoneum is involved in about 80% of all perforated bladders. Communication with the peritoneal cavity is more uncommon.
Blunt or perforating traumas associated with fractures of pelvic bones are the most frequent causes of perforation. Catheter insertion or biopsy procedures are less common traumatic agents.
CT-excretory phase permits to reveal the breach of the wall and the extent of the extravasation in the majority of cases. A retroperitoneal perforation is associated with higher values of HU density compared to intraperitoneal perforation. Typically, fluid and air collections spread in the perivesical space.