urinothorax is associated with obstructive uropathy after trauma or surgery

Differentiating transudative from exudative effusions is useful in two ways: The differential diagnosis for transudates is much shorter, and the fluid itself is rarely problematic unless large in volume. This patient’s transudate does not have an obvious cause, but there is a clue that some of the data may be incorrect. Repeating a thoracentesis and sending the sample for several unique tests would confirm the diagnosis, which in this case is caused by urine. Urinothorax is an uncommon cause of transudative pleural effusions and is usually associated with obstructive uropathies but can also develop after trauma or be iatrogenic. It is typically characterized as meeting transudative criteria but with a ratio of pleural to serum creatinin >1.0, along with a low pleural pH. These criteria can make the diagnosis, and technetium 99m renal scans can identify the source of the urine leak. Checking pleural creatinine is not a standard test on pleural effusions but would be helpful in this situation. Pleural pH is more commonly measured but often processed improperly. This patient’s pleural pH of 7.51 suggests either a profound metabolic alkalosis not represented on his serum chemistry panel or an inaccurate measurement. The latter is more likely because pleural fluid sent for pH requires the sample be stored anaerobically and processed within 4 h. Samples are often stored in capped vials containing significant amounts of air. Delays in processing compounded by aerobic storage methods can dramatically raise pH levels, providing misleading information. Historically, storing pleural fluid samples on ice was recommended, but recent studies suggest this is unnecessary. Of note, both lidocaine and heparin in storage tubes can lower the fluid’s pH. A repeat sample processed correctly would reveal a low pH and an opportunity to measure the pleural creatinine level. Another possibility for his transudate is a leak of cerebrospinal fluid resulting from his earlier traumatic injury. The presence of β-2-transferrin in pleural fluid is highly suggestive of a duropleural fistula.1

42-year-old man is referred for further evaluation of a recurrent pleural effusion. He reports no history of breathing difficulties or respiratory health problems but has noticed dyspnea in the past 4 months for which he sought medical attention. He reports he had a collection of fluid around his right lung that was sampled last month and that it was “clear.” He brings a copy of the test results (Figure 1) and a copy of a recent chest radiograph demonstrating a moderate right pleural effusion but otherwise normal. He reports no fevers, chills, sweats, orthopnea, or lower extremity swelling. The patient reports being in good health except for injuries sustained during a car crash last year that involved several orthopedic and abdominal surgeries. He reports no chronic health conditions and takes no medications. He reports drinking one or two beers on weekends, claims to be a lifelong nonsmoker, and reports no recreational drug use. He is sexually active with one partner for the past 16 years.

On physical examination, the patient is alert and oriented to person, place, and time. His vital signs are as follows: BP, 124/70 mm Hg; heart rate, 74/min; respiratory rate, 12/min; SpO2, 97% on room air; temperature, 36.8°C; and BMI, 26 kg/m2. There are no jaundice or skin rashes. The nasal/oropharynx examination is normal. There are no neck masses, jugular venous distension, or palpable lymph nodes. His chest is normal to inspection, with a dull right base to auscultation and percussion but no adventitious sounds. There are no heart murmurs, rubs, or gallops. There is a large ventral abdominal scar that is well healed, with active bowel sounds and without guarding or rebound. There is no palpable organomegaly. There are several scars on the extremities from external fixators, which are warm and dry, with no edema. Dorsalis pedis pulses bilaterally are strong.

The effusion in the current case has low pleural fluid protein and lactate dehydrogenase to serum ratios and is a transudate with a very low glucose. There are only a handful of conditions that typically cause transudative pleural effusions: volume overload, heart failure, cirrhosis, and nephrotic syndrome. Less common conditions include iatrogenic infusion of crystalloids into the pleural or peritoneal space and urinothorax. Nephrostomy tube placement, pelvic trauma, and surgery in the pelvis or retroperitoneum can occasionally be complicated by injury to the renal calyces, ureters, or bladder. When this occurs, urine can flow into the peritoneal or retroperitoneal spaces and find its way into the lower pressure pleural space. The majority of such patients, like the patient in this case, are oliguric. The pleural fluid characteristics depend not only on the characteristics of the urine leaking into the pleural space but also on the effects of local tissue trauma. Although urinothoraces are classically transudates, they may be exudative in up to 40% of cases. Also, urinothoraces may be bloody, neutrophilic or lymphocytic, and have low or high pH and glucose. Therefore, the only characteristic that reliably differentiates a urinothorax from other causes of pleural effusion is the ratio of pleural fluid to serum creatinine of >1. Therapeutic pleural drainage is temporizing until definitive correction of the injury can occur. This patient sustained an injury to her left ureter during surgery. She required reexploration and a ureteral repair.

Malposition of a subclavian venous catheter can cause acute massive hemothorax or hydrothorax. Once a catheter has been removed, however, contrast venography would only be useful in patients who are actively bleeding, which was not the case in this patient (answer B is incorrect).

An esophageal injury following the placement of a nasogastric tube would produce an exudative effusion with a high pleural fluid amylase. But because this effusion was transudative, a pleural fluid amylase would not be useful.

Chylothorax is a rare complication of abdominal surgery. In such cases, injury to the intestinal lymph trunks or cisterna chyli can cause pink, milky, triglyceride-rich chyle to leak into the peritoneum and pleural spaces through diaphragmatic pores. However, the clear fluid in this case was not consistent with chyle.

Finally, this patient’s history of rheumatoid arthritis was irrelevant. Rheumatoid arthritis causes exudative effusions not transudative effusions.2345

A 65-year-old woman with a history of rheumatoid arthritis had a radical hysterectomy for endometrial carcinoma. Her estimated blood loss during the procedure was 500 mL for which she received 2.5 L of lactated Ringer’s solution via a left subclavian venous catheter. The next morning, she is a little dyspneic and in pain but is otherwise doing OK. Both her subclavian catheter and her nasogastric tube are removed per protocol. Later in the afternoon, she becomes progressively more short of breath and is transferred to the ICU. On arrival, her vital signs are as follows: BP, 120/85 mm Hg; heart rate, 110/min; respiration, 35/min; temperature, 36.2°C; and urine output, 0.2 mL/kg/h. A chest radiograph is obtained (Figure 1), followed by an ultrasound-guided thoracentesis. Serology and pleural fluid characteristics are as follows: (Figure 2). 

Which of the following tests will most likely lead to the diagnosis?

Footnotes

  1. SEEK Questionnaires ↩

  2. Griffo S, De Luca G, Stassano P. Chylothorax after abdominal surgery. Gen Thorac Cardiovasc Surg. 2010;58(3):159-162. PubMed ↩

  3. Numata Y, Ishii K, Seki H, et al. Perforation of abdominal esophagus following nasogastric feeding tube intubation: a case report. Int J Surg Case Rep. 2018;45:67-71. PubMed ↩

  4. Steiger MJ, Morgan AG. Diagnostic aspiration of an iatrogenic hydrothorax following subclavian catheterization. Postgrad Med J. 1990;66(778):672-673. PubMed ↩

  5. Toubes ME, Lama A, Ferreiro L, et al. Urinothorax: a systematic review. J Thorac Dis. 2017;9(5):1209-1218. PubMed ↩