Modalities for the diagnosis of abdominal and thoracic cavity defects in patients on peritoneal dialysis

INTRODUCTION — The presence of dialysis fluid in the abdominal cavity increases intra-abdominal pressure and may lead to the dialysis fluid leaking from acquired or congenital defects in the abdominal and thoracic wall. This may manifest as hydrothorax, hernia, or genital/abdominal wall edema.

Various diagnostic modalities were previously used to help diagnose these defects. In the 1970s, plain radiographs, contrast catheterograms, and peritoneographs were commonly utilized. However, since they were somewhat inaccurate and misleading [1], these techniques have been replaced by radiologic methods. These newer methods include nuclear isotope scans (peritoneal scintigraphy), computed tomography scans (CTS; CT peritoneography [CTP]), and magnetic resonance imaging (MRI; MR peritoneography [MRP]) using contrast/dye materials.

This topic review will discuss diagnostic methods used to detect defects in the abdominal and thoracic wall among patients undergoing peritoneal dialysis. The clinical manifestations suggestive of a hernia or peritoneal and/or pleural leak are reviewed elsewhere:

●(See "Abdominal wall hernia and dialysate leak in peritoneal dialysis patients".)

●(See "Noninfectious complications of peritoneal dialysis catheters".)

●(See "Noninfectious complications of continuous peritoneal dialysis".)

PERITONEAL SCINTIGRAPHY — Peritoneal scintigraphy is a safe, accurate, and rapid way of diagnosing leaks in the peritoneal cavity [2-5]. Three to 5 millicuries of technetium 99m isotope per 0.5 to 2.0 L of dialysis solution is injected into the abdominal cavity. Multiple projections (anterior, lateral, posterior, and oblique) are then taken to help separate a leak in the abdominal wall from the peritoneal fluid posterior to it [6].

Although a significant dose of isotope is used, it is not absorbed from the peritoneum, and almost all of the material drains out of the body after the procedure. The net dose of radiation is therefore only a fraction of the total dose instilled into the peritoneal cavity [7].

Various radioligands that have been used include sulfur colloid, albumin colloid, tin colloid, and macroaggregated albumin colloid (MAA). The size of these molecules is larger than mesothelial pores in the diaphragm that communicate with the lymphatic vessels, thus preventing their uptake as well as maintaining good intraperitoneal concentration [8].

To facilitate fluid egress out of the peritoneal cavity and thus enhance diagnostic sensitivity, a variety of measures can be employed to increase intra-abdominal pressures [9]. The patient should ambulate or (if nonambulatory) be made to roll from side to side. Use of larger volumes, if tolerated, should also be advocated. Images are subsequently taken at regular time intervals, with most leaks being detected in two to six hours. Delayed scans (24 to 48 hours later) are advocated in small leaks or in initially equivocal studies [6,10].

Peritoneal scintigraphy is not only useful in diagnosing leaks, hernias, and hydrothorax (image 1 and image 2) but can also demonstrate the inflow and distribution of dialysis fluid in the peritoneal cavity. In addition, it can facilitate repeated examination of the area of interest, if clinically indicated. This technique has also been found to be useful in the diagnosis of adhesions in the peritoneal cavity [11].

CT SCANS AND CT PERITONEOGRAPHY — Computed tomography scans (CTS) and CT peritoneography (CTP) are accurate and reliable methods of diagnosing peritoneal defects. However, CTP, which is performed using dialysis fluid mixed with iodinated contrast, has a distinct advantage over CTS for diagnosing small leaks, adhesions, loculated fluid collections, intra-abdominal abscesses, and pseudocysts [10,12,13].

Preparation for this diagnostic procedure is similar to that done for peritoneal scintigraphy. The dose of iodinated contrast used is approximately 50 mL per liter of dialysis fluid. Oral and intravenous (IV) contrast can be simultaneously given to diagnose any abscesses or tumors [10].

Besides diagnosing leaks and defects in the abdominal and thoracic wall, quantification of dialysis fluid and its distribution with respect to catheter position in the peritoneal cavity can also be done with considerable diagnostic accuracy (this method slightly underestimates the volume of fluid) [10]. CTP is not effective in diagnosing fibrinous catheter obstruction or obstruction of the catheter by adhesions or omentum [12]. Techniques that increase the pleuroperitoneal pressure gradient (breathing maximally and straining) may enhance the sensitivity of CTP in the diagnosis of pleuroperitoneal communications [14]. Radiation exposure may be of concern in pediatric populations.

MRI AND MR PERITONEOGRAPHY — Magnetic resonance imaging (MRI) and MR peritoneography (MRP) are additional modalities to help diagnose these anatomic defects [15-17]. Gadolinium-based dye was most commonly used.

However, among patients with moderate to advanced kidney disease (dialysis dependent or estimated glomerular filtration rate [eGFR] <30 mL/min), the administration of gadolinium has been associated with the potentially severe syndrome of nephrogenic systemic fibrosis. In such patients, gadolinium-based imaging should be avoided, if possible. This is discussed separately. (See "Nephrogenic systemic fibrosis/nephrogenic fibrosing dermopathy in advanced kidney disease".)

Saline, or the dialysis solution itself, has also been used as contrast medium [17]. These fluids show up as a hyperintense image on T2-weighted images owing to its electrolyte content. The use of dialysis fluid as contrast avoids the risk of catheter contamination during the procedure. It also does not require the presence of specialized personnel to instill the dye into the peritoneum. In addition, the absence of dye makes the procedure cheaper. MRP provides multiplanar images, and its diagnostic accuracy is similar to that of computed tomographic peritoneography (CTP) [17].

CLINICAL METHODS — Clinical methods of diagnosing hydrothorax and abdominal wall leaks may be easy to perform but may not be sensitive enough to diagnose these defects.

Thoracentesis — Thoracentesis is a simple, although invasive, method to diagnose hydrothorax. It is especially helpful in patients who are acutely symptomatic, a setting in which this procedure can be diagnostic as well as therapeutic. (See "Ultrasound-guided thoracentesis".)

The slight but real risks of thoracentesis make this procedure a less attractive method of diagnosis. It becomes an attractive option in cases of extreme symptoms due to large pleural effusions.

If thoracentesis is performed, dialysate fluid in the pleura should have a higher concentration of glucose than plasma, and the concentrations of lactate dehydrogenase (LDH) and protein are consistent with a transudate [18]. A cell count and cultures (to exclude infection) and L and D isomers of lactate (if available) should also be performed. The L isomer of lactate is endogenous, while commercial dialysis solutions have both L and D isomers; as a result, if the D isomer of lactate is present in the pleural effusion, the source is the commercial dialysate [19]. (See "Pleural fluid analysis in adults with a pleural effusion".)

Methylene blue dye — Instillation of methylene blue dye into the peritoneum has also been found useful in diagnosing leaks. However, there have been some case reports of irritation to the abdominal viscera [20].

Clinical observation — An easier but relatively insensitive method of diagnosing hydrothorax is to keep the abdomen dry overnight and to repeat a chest radiograph in the morning to determine if the pleural effusion has decreased.

Biochemical analysis — Biochemical analysis for glucose and lactate can be performed on the fluid that has leaked into the abdominal wall.

Alternative peritoneal dialysis solutions, however, such as icodextrin, may not contain glucose. In this setting, the addition of povidone-iodine to a fluid aspirate may result in a characteristic blue-black color [21].

SUMMARY AND RECOMMENDATIONS

●Dialysate leaks in patients on peritoneal dialysis– The presence of dialysis fluid in the abdominal cavity increases intra-abdominal pressure and may lead to the dialysis fluid leaking from acquired or congenital defects in the abdominal and thoracic wall. Different diagnostic modalities can be used alone or in combination to diagnose these defects. (See 'Introduction' above.)

●Computed tomographic peritoneography – Based on sensitivity, specificity, and cost, we use and recommend computed tomographic peritoneography (CTP) as the initial study to diagnose abdominal wall and/or thoracic defects in most patients on peritoneal dialysis. It is the most commonly used modality in the United States and offers distinct advantage over plain CT scans.

●Other imaging studies – Other imaging studies include magnetic resonance peritoneography and peritoneal scintigraphy.

•Magnetic resonance peritoneography – Although magnetic resonance peritoneography (MRP) has a similar sensitivity to CTP in diagnosing these defects, the administration of gadolinium among patients on dialysis has been associated with the potentially severe syndrome of nephrogenic systemic fibrosis. In such patients, gadolinium-based imaging should therefore be avoided. MRP using dialysis fluid as a contrast medium may eventually offer a valuable, cheap, and user-friendly alternative. However, further study in additional centers is required to validate its usefulness. (See 'MRI and MR peritoneography' above.)

•Peritoneal scintigraphy – Isotope scanning is principally used in patients who are allergic to iodinated contrast used in CTP. (See 'Peritoneal scintigraphy' above.)

●Clinical methods – A variety of clinical methods of diagnosing hydrothorax and abdominal wall leaks may be easy to perform but may lack the necessary sensitivity for diagnosis. (See 'Clinical methods' above.)