Keywords
peritoneal scintigraphy - SPECT/CT - pleuroperitoneal fistula - diaphragmatic defect
- peritoneal dialysis catheter
Introduction
Although uncommon, hydrothorax is a recognized complication of peritoneal dialysis
first described in 1967, occurring in approximately 2% of continuous ambulatory peritoneal
dialysis patients.[1]
[2] Hydrothorax is usually a clear transudative (mostly right-sided) pleural effusion,
which should be differentiated from other sources of pleural effusion, such as heart
failure or fluid overload, causing increased hydrostatic pressure in the lungs.[3] Pathogenesis of peritoneal dialysis catheter-associated hydrothorax has been reported
to originate from congenital or acquired defects of the diaphragm, defective lymphatic
drainage, and pleuroperitoneal communication via a fistulous tract.[4]
Various tools for diagnosing hydrothorax have been evaluated with thoracentesis used
to differentiate between transudative and exudative pleural fluid. However, those
methods can identify the composition of the fluid but cannot establish the origin
of it beyond a doubt. This is where imaging comes into play. Among the various imaging
techniques, the ones available for examining the peritoneal cavity include chest radiographs,
magnetic resonance imaging (MRI), computed tomography (CT) with iodinated contrast
and peritoneal scintigraphy utilizing radiotracer with moderate-to-large volume dialysate
or normal saline. The case described here demonstrates the diagnosis of pleuroperitoneal
fistula utilizing low-dose single-photon emission computed tomography (SPECT/CT) in
peritoneal scintigraphy with low-volume normal saline and radiotracer.
Case Presentation
Our patient is a 39-year-old male with a history of end-stage renal disease secondary
to focal segmental glomerulosclerosis on peritoneal dialysis. He presented to the
emergency department complaining of 1 week of severe shortness of breath and chest
pain with physical exam revealing decreased breath sounds on the right chest. The
initial chest radiograph ([Fig. 1]) demonstrated a large right pleural effusion that prompted an emergent ultrasound-guided
thoracentesis with the aid of interventional radiology. Thoracentesis resulted in
1.3 L of clear fluid with further analysis showing the fluid to be transudative demonstrating
a pleural fluid to serum creatinine ratio greater than 1.0 and pleural fluid to serum
glucose ratio over 5.0. These findings raised suspicions for peritoneal dialysis-related
hydrothorax secondary to a pleuroperitoneal fistula.
Fig. 1 Anterior–posterior (A) and lateral (B) chest radiograph demonstrating a large right pleural effusion with adjacent atelectasis
before thoracentesis.
Next, the patient presented to the nuclear medicine department with a peritoneal dialysis
catheter in place. To limit the amount of administered intraperitoneal fluid, 100 mL
of normal saline and 3.3 mCi of Tc-99m sulfur colloid (SC) were instilled in the peritoneal
cavity. Instead of static imaging, 1-minute anterior and posterior dynamic images
of the mid-chest and upper abdomen were acquired for 30 minutes, immediately followed
by a low-dose SPECT/CT of the mid-chest and upper abdomen.
The dynamic acquisition ([Fig. 2]) demonstrated prompt flow of radiotracer in the peritoneal cavity with tracer noted
in the subdiaphragmatic space and absence of substantial extravasation into the thorax.
Upon separate examination of the SPECT/CT with a significantly narrow window, radiotracer
migration was also noted in the right hemithorax ([Fig. 3]). Following confirmation of pleuroperitoneal fistula, peritoneal dialysis was discontinued,
and hemodialysis was immediately initiated.
Fig. 2 Anterior and posterior dynamic images that demonstrate the flow of radiotracer in
the perihepatic and right subdiaphragmatic space of the peritoneal cavity with the
absence of notable extravasation into the thorax.
Fig. 3 Coronal and sagittal fused single-photon emission computed tomography/computed tomography
images with radiotracer activity in the right hemithorax (arrows).
Discussion
Peritoneal dialysis-associated hydrothorax is an uncommon yet challenging complication
that can be severe and life-threatening, making timely diagnosis imperative.[4] Often, the etiology of such effusions remains unclear, despite diagnostic imaging
and laboratory analysis of fluid obtained via thoracentesis. Pleural fluid analysis
showing a high glucose content can indicate peritoneal fluid, although the origin
is not definite.[4]
[5] Due to this fact, medical imaging plays a crucial role in confirming the source
of the pleural fluid.
CT and MR peritoneography are valuable modalities for determining whether an anatomic
diaphragmatic defect is present.[3] Between CT and MR, the reference standard is CT peritoneography using intraperitoneal
contrast, which has a greater spatial resolution, widespread availability, and relatively
low cost capable of depicting the entire peritoneal cavity.[3]
[6] Primary disadvantages include namely exposure to ionizing radiation and iodinated
contrast media, which pose the risk of an allergic reaction and peritonitis. Furthermore,
it has been reported that CT peritoneography shows a 33% sensitivity in identifying
pleuroperitoneal leak.[3]
[7]
[8]
[9] MRI peritoneography is an effective method for detecting complications of peritoneal
dialysis catheters by evaluating the diaphragm with the absence of radiation exposure,
which is its most significant advantage when compared with CT peritoneography or peritoneal
scintigraphy. Its disadvantages include a higher cost and limited availability than
those typical of other modalities.[6]
Peritoneal scintigraphy using radiopharmaceuticals such as Tc-99m SC, Tc-99m macroaggregated
albumin, and Tc-99m albumin colloid has been shown to be efficient methods for showing
peritoneal leakage.[7]
[8]
[10] Tc-99m SC was the preferred radiopharmaceutical in this case because it was readily
available. Most scintigraphic protocols described in the literature obtain initial
dynamic planar imaging following the administration of tracer and 350 to 2,500 mL
of dialysate or normal saline, without or with delayed images that can be obtained
up to 24 hours later.[7]
[8]
[10]
[11]
[12]
[13]
[14] Delayed imaging of leaks is frequently necessary; however, it is not always feasible
in CT peritoneography because the prolonged presence of an iodinated contrast medium
increases the chance of peritonitis.[15] Although there is some radiation exposure, which is minimal, scintigraphy offers
the advantages of low cost, no risk of an allergic reaction, or peritonitis. It is
also easy to perform and has a higher degree of sensitivity ranging from 40 to 50%
to detect relatively small volumes of leakage without morbidity.[4]
[9]
[15]
[16]
As demonstrated in this case, planar and dynamic images may not have enough spatial
resolution to definitively determine the presence of a radiotracer within the pleural
fluid, making SPECT/CT an ideal option. The main advantage of SPECT/CT is the increased
specificity achieved through more precise characterization of functional findings.[17]
[18]
[19] The low-dose CT in the SPECT/CT imaging is used to localize SPECT lesions with low
radiation doses of 1 to 4 mSv.[19]
Lymphatic drainage of the peritoneal space drains to the celiac, superior mesenteric,
and periportal lymph node group. The lymph continues via the thoracic duct into the
mediastinal nodes.[20] Metastases can reach the mediastinum from the retroperitoneal lymph nodes, and from
the peritoneal cavity through the diaphragm, which has a rich subperitoneal lymphatic
network.[21] Lymphoscintigraphy is used in gynecologic cancer patients to evaluate transdiaphragmatic
lymphatic drainage. Lymph node uptake was excluded because this patient does not have
a history of malignancy. SPECT/CT utilization also helped localize whether the uptake
was in the pleural space versus the mediastinal nodes.
Conclusion
In summary, peritoneal scintigraphy plays an essential role in diagnosing peritoneal
dialysis catheter-related complications such as a pleuroperitoneal fistula leading
to hydrothorax, avoiding delay in diagnosis, which can lead to a worsening clinical
status. Upon diagnosis, therapeutic options include a therapeutic thoracentesis with
discontinuation of peritoneal dialysis or surgical intervention for diaphragmatic
repair. In this patient, the pressure gradient between the peritoneum and pleura probably
drove dialysate across the diaphragmatic defect. This case demonstrates that in the
absence of ascites, the instillation of a small volume normal saline with Tc-99m SC
in conjunction with SPECT/CT can definitively determine the etiology of hydrothorax
to be due to a pleuroperitoneal communication.
