Emphysematous Hepatitis
Emphysematous hepatitis (EH) is a rare condition characterised by imaging findings of progressive replacement of hepatic parenchyma by gas with out any fluid component or mass effect (5).
Differential Diagnosis/Mimics:
1. Pyogenic liver abscess (PLA), where the fluid component is the fundamental difference between PLA and EH (7). Pyogenic hepatic abscesses on CT are typically encapsulated hypo-densities exerting mass effect on adjacent structures which may 'cluster' or multiple lesions coalescing into a single larger lesion. Occasionally PLAs will contain gas bubbles or gas-fluid level(s) (7).
2. Hepatic infarction (8) – CT typically presents a peripherally located ill-defined wedge region of hypo attenuation, without associated mass effect.
Emphysematous Cholecystitis
Emphysematous cholecystitis (EC) is an unusual form of acute cholecystitis. It is a surgical emergency with a high risk of gallbladder gangrene and perforation. Unlike typical calculous cholecystitis, EC is primarily a vascular occlusive event with cystic artery compromise (1).
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Imaging characteristics of EC are the presence of intraluminal gas. Other distinctive imaging features include gas within the gallbladder lumen, and peri-cholecysitic tissues (9).
Not all gas within the gallbladder lumen and the wall is EC. Differential diagnosis includes; fissured gallstones, iatrogenic, and spontaneous biliary fistula (9).
Emphysematous Pancreatitis
Emphysematous pancreatitis (EP) is a rare complication of severe acute pancreatitis, with the necrotic pancreatic parenchyma replaced by gas (10). CT imaging features include; indistinct pancreatic outline, focal or diffuse parenchymal enlargement with poor enhancement, a mottled collection of gas replacing the pancreatic parenchyma.
Gas within the pancreas is not definitive for EP and may also occur from other processes, including: infected pseudocysts, abscesses, benign and iatrogenic fistulas as well as malignant processes (10).
Pylephlebitis
Ascending septic thrombophlebitis is an uncommon suppurative thrombotic occlusion of the portal vein or its branches(11). CT imaging commonly shows a distinctive central hypodense portal-mesenteric-venous thrombus or gas. The liver may demonstrate parenchymal attenuation differences and intrahepatic abscesses. CT may identify the precipitating focus of infection.
Pyelphlebitis is most commonly a complication of an infection in a region that drains into the portal venous system e.g. diverticulitis and peritonitis.
Urinary Tract Emphysema
Emphysematous pyelonephritis is characterised by gas within the renal parenchyma as well as the collecting system. It has a poor prognosis and requires prompt antimicrobial treatment and emergent drainage or removal of the infected kidney (1, 2).
Emphysematous cystitis, characterised by gas within the bladder wall and lumen, is less severe and up to 90% can be treated with catheterisation, antibiotics and treatment of underlying conditions (3).
Emphysematous pyelitis, in which gas is limited to the ureters and calyces, is a relatively benign entity. With prompt medical therapy the prognosis is excellent (1, 4).
The principal differential for gas within the urinary tract is instrumentation, although trauma and fistulae are also potential causes (1).
Female Genital Tract Emphysema
Emphysematous vaginitis is rare. It presents with vaginal discharge and may be related to Trichomonas vaginalis (12). On imaging it is characterised by the presence of multiple gas-filled cysts. It is generally self-limiting and benign.
Gas gangrene of the uterus is a rare condition and most commonly results from a primary infection in the puerperium or from necrosis and secondary infection of a uterine tumour. The severity of the condition varies on the extent of the infection, with involvement of the myometrium requiring hysterectomy.
The differential for gas within the female genital tract is similar to that of the urinary tract, with instrumentation, fistulae and recent sexual intercourse all possible causes (1).
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Emphysematous Prostatitis
Emphysematous prostatitis carries a significant mortality(13). Urinary retention and indwelling catheters are predisposing factors. The abscess may be drained via either transurethral or transrectal route. Where urinary retention exists suprapubic catheterisation may be preferred to avoid seeding of infection.
Fournier’s Gangrene
Defined as a necrotizing fasciitis of the external genitalia, perineum or perianal region, Fournier’s gangrene has a high mortality without emergency surgical debridement and antimicrobial treatment (1). CT shows soft tissue inflammation and subcutaneous emphysema.
Emphysematous Gastritis
The stomach is the least common location for intramural gas in the GI tract (14).
Gastric emphysema and emphysematous gastritis (EG) share similar imaging appearances but are distinct entities. Gastric emphysema is generally a benign, self-limiting disease whilst EG refers specifically to infectious gastritis (15).
Aetiology can broadly based into two categories: primary gastric pathology and intra-abdominal pathology arising for other hollow viscera (14). Distinguishing gastric pneumatosis due to EG or ischemia from more benign aetiologies requires clinical assessment as there are no definitive imaging differences(14).
Pneumatosis Intestinalis
Pneumatosis intestinalis is not a disease but a sign which is defined as the presence of gas within the bowel wall: it is associated with numerous conditions, ranging from benign to life-threatening(16). The exact pathogenesis is unclear. Features suggestive of a life threatening cause include: poor mural enhancement, vascular occlusion, free fluid, porto-mesenteric venous gas and distribution in a vascular territory(16).
Musculoskeletal
The bony pelvis, spine and abdominal wall are at risk of being overlooked as they are on the edge of the busy intraabdominal cavity. Abnormalities outside area of interest account for 7% of radiologic error (17). By exploring causes of gas in these structures this section provides review areas for the radiologist.
Bone:
Intraosseous gas when seen in the extra axial skeleton is pathognomonic for emphysematous osteomyelitis.
However, when seen in the vertebral bodies it is almost always due to a non-infectious cause.
In young patients with no comorbidities or recent surgery then Fusobacterium necrophorum should be considered and an oropharyngeal source should be sought. Polymicrobial infections are more common in cases of contiguous spread from intraabdominal source or recent surgery (18).
Paravertebral/pelvic soft tissues:
Pneumoretroperitoneum can be caused by retroperitoneal viscus perforation, abscess or residual post-operative gas.
The psoas muscle forms the posterior boundary of the retroperitoneal space. Psoas abscesses are mostly secondary to contiguous spread from bowel, kidney or bone and thus have the same microbiological differential (6).
Abdominal wall:
Gas within the abdominal wall can be broadly categorised into iatrogenic, infection or fistulation. Iatrogenic abdominal wall emphysema can range greatly in volume depending on the cause.
Enterocutaneous fistulation is most commonly secondary to abdominal surgery. Other aetiologies include: inflammatory bowel disease, tumours and radiation enteritis (19).
Fistulation can be complicated by life threatening necrotising fasciitis
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