Over a period of 6 years (2007 – 2013) a 60-year old man with chronic renal insufficiency be-cause of autosomal-dominant polycystic kidney disease (APDKD) was treated by continuous ambulatory peritoneal dialysis (CAPD). In the course of his treatment he experienced 2 culture proven peritonitic events (due to taenia saginata in 2009 and staphylococcus lentus in 2012) without evidence for tunnel infection. Clinical examination revealed no fever, a soft abdomen with no pain, no tenderness or resistance on palpation. Ultrasound of the abdomen showed the intraperitoneally located catheter (Fig 1).
A large cystic lesion was detected on B-mode ultrasound with thick capsule wall (Fig 2).
After the intraperitoneally administration of SonoVue® the distribution of the contrast agent was evaluated. The entire pseudocystic lesion was rapidly and homogenously enhanced (Fig 3).
Contrast enhanced ultrasound (CEUS) with high frequency probe showed in the near field that the lesion was extraperitoneally located (Fig 4).
CT showed the instilled dialysate entrapped in a cyst that enclosed the inner tip of the Tenck-hoff catheter (Fig 5).
The suspected diagnosis was peritoneal pseudocyst. An exploratory laparotomy was per-formed followed by surgical removal of the catheter with excision of the pseudocystic wall. Histologic examination of the excised cyst showed postsurgical a much smaller diameter (5.5 x 3.5 cm in size) with smooth surface. Its wall was about 0.2 – 0.3 cm thick with grey and white colors. Histology revealed sclerotic tissue with reactive changes and fibrinous elements caused by the inflammatory pseudocapsule. No evidence of malignancy was found. To date, he is in good clinical condition with stable kidney function under hemodialysis therapy. The final diagnosis was peritoneal pseudocyst.
Intraperitoneal pseudocyst formation is an uncommon complication of peritonitis in patients on CAPD and also in patients with ventriculo-peritoneal shunts (the most successful method for managing hydrocephalus) [(4, 5)]. The main complications of peritoneal dialysis (PD) ther-apy include catheter dysfunction (mainly caused by leakage, obstruction or malposition), in-adequacy of dialysis because of ultrafiltration failure, infection complications caused by peri-tonitis or tunnel or exit-site infections and hernias [(4, 6)]. The exact cause and pathophysiolo-gy of abdominal pseudocysts is still debated [(5)]. Predisposing factors for pseudocyst for-mations are: bacterial infections and abdominal surgery. In the case of ventriculo-peritoneal associated abdominal pseudocysts multiple shunt revisions, silicon allergy and prior shunt in-fection are discussed [(6)]. The most common intra-abdominal response to infection is the sheathing of the peritoneal catheter. Abdominal pseudocysts are distinct from encapsulated peritoneal sclerosis (EPS) and represent a distinctive complication of PD. Formation of a pseu-docyst around the tip of an intraperitoneal catheter has been described previously as a rare (incidence, 1 % - 4 %) complication of ventriculo-peritoneal shunts in the treatment of hydro-cephalus [(7)]. In the case of simultaneous decrease in dialysis solution inflow and dialysate outflow combined with decreases in dialysis adequacy after peritonic events, one should keep in mind the possibility of a fibrous pseudocyst enclosing the intraperitoneal catheter. The clin-ical presentation may resemble that of an acute abdomen including abdominal pain with or without a palpable mass, abdominal distension and tenderness, nausea and vomiting, consti-pation, fever and signs of shunt malfunction [(8, 9)].
As a differential diagnosis, EPS is also a serious and rare complication of long-term PD thera-py with high mortality. EPS is associated with the duration of PD and the number of peritonitis events [(10)]. Pseudocyst formation has not been described so far in EPS. Mortality in EPS is high, often caused by malnutrition and sepsis, whereas the outcome in our patients was excel-lent. Taken together, these observations make EPS unlikely in our patient [(5)]. Some clinical features, such as abdominal pain, weight loss and elevated inflammatory markers levels may occur in EPS [(10)]. However EPS is defined by partial bowel obstruction and encapsulated bowel loops as a result of sclerotic thickening of peritoneal membrane, consisting of dense layers of fibro-connective tissue infiltrated by mononuclear cells. Bowel obstruction was not present in our patient and histological features of the abdominal pseudocyst were different from that of EPS.
Ultrasound (US) is an easy way for a quick and reliable diagnosis of abdominal pseudocysts. Pseudocysts can be differentiated from ascites by their characteristic displacement of the gas containing bowel loops using ultrasound and conventional abdominal X-ray as well as by com-puted tomography. The absence of shifting dullness is also a helpful sign for diagnosis [(8)]. US is able to demonstrate the presence of localized peritoneal fluid collections as well as its size, contents and relations of the catheter to the wall. Sonographic signs include an echofree mass with or without septations. Peritoneal pseudocysts can be visualized as smooth echo-free fluid collection with pseudo-membrane. Ultrasound can also be used to percutaneously drain the pseudocysts [(4)]. Sometimes ultrasound failed to delineate the cyst due to its large size, favouring the diagnosis of ascites secondary to sclerotic peritonitis. CEUS applied intravenously is nowadays a well-established imaging modality in the evaluation of liver, kidney, gastrointestinal tract and vascular imaging [(11-16)]. CEUS could well differ-entiate cysts from solid or solid-cystic lesions. Besides the conventional intravenous injection of contrast agents SonoVue can be administered intraperitoneally showing the distribution of the contrast agent indicating the extent of the pseudocyst. CEUS examined with the high fre-quency probe could also clearly show if the lesion location was peritoneal or extraperitoneal. Herewith we discuss features of abdominal pseudocysts and the role of extravascular and in-tracavitary contrast enhanced ultrasound (evCEUS) in its diagnosis and differential diagnosis. Extravascular contrast enhanced ultrasound has been applied for many indications including percutaneous cholangiography and drainage [(17, 18)], abscess evaluation [(19, 20)], nephros-tomy [(21)] and examination of Zenker’s diverticulum [(22)] and perineal applications [(23, 24)]. We refer to other cases of the month from our group [www.efsumb.org]. Major ad-vantages of this method include the lack of radiation exposure, high detail resolution and real time imaging as the additional beneficial features of CEUS. The treatment involves exploratory laparotomy followed by surgical removal of the catheter with or without excision of the pseudocyst wall [(25)]. The treatment in neurosurgery is either sonographically guided aspiration of the trapped fluid or surgical replacement of the ventricu-lo-peritoneal shunt [(4, 26)]. Infected cysts generally resolve with antibiotics and surgical management. In the case of ventriculo-peritoneal shunt associated pseudocysts obstruction of the distal catheter must be treated as an emergency because it can lead to a significant in-crease in intracranial pressure, resulting in associated complications that can cause consider-able morbidity and possibly death. Overall mortality and prognosis appear to be good, alt-hough in our patient, the pseudocyst led to conversion to hemodialysis therapy.