Case In Point: A man with renal failure, dyspnea, and an apparent lung mass

The case

A 54-year-old man with chronic renal insufficiency presented with shortness of breath, nonproductive cough, and chest pain. The patient had hypertension, type 2 diabetes mellitus, and a 30-pack-year history of cigarette smoking. He denied alcohol or illicit drug use and prolonged exposure to asbestos, chemicals, or fumes.

Physical examination revealed normal vital signs. On chest auscultation, bilateral inspiratory crackles were heard. Findings from the cardiovascular examination were normal, including the ab-sence of jugular venous distention. Bilateral pitting edema was present. Funduscopic examination revealed photocoagulation burns for diabetic retinopathy.

The patient's serum creatinine level was 3.5 mg/dL, and his albumin level was 3 g/dL. Cardiac enzyme markers and an ECG did not show any evidence of recent cardiac ischemia.

The chest radiograph demonstrated an apparent right lung mass (Figure 1). A CT scan of the chest showed a 7.6 3 5.6-cm homogeneous, oval density within the right horizontal fissure (Figure 2). The patient's echocardiogram demonstrated mild left ventricular systolic dysfunction with an ejection fraction of 45% to 49%; there was no evidence of pericardial effusion or valvular abnormality.

The patient was treated with diuretics and fluid restriction without resolution of symptoms. Serum creatinine and urea nitrogen levels continued to rise, with accompanying oliguria. On the third day of hospitalization, hemodialysis was initiated. Three days later, a follow-up chest radiograph revealed significant resolution of the lung mass (Figure 3).

Discussion

The transient collection of pleural fluid within an interlobar fissure has been referred to as "vanishing tumor," "phantom tumor," and "pseudotumor."^1-3 Pseudotumors occur when pleuritis is associated with the alteration of the Starling forces regulating interstitial fluid volume. Pleuritis leads to adhesions in the pleural space, which prevent the free accumulation of fluid.

In the presence of renal, heart, or hepatic failure, a localized pleural effusion may appear as a pulmonary pseudotumor.^4-6 Pseudotumors can also occur secondary to exudates from parapneumonic effusions, tuberculosis, connective tissue diseases, and malignancy. Interestingly, 80% of pseudotumors occur in the horizontal fissure in the right lung; left-sided pseudotumors are rare.

Pulmonary pseudotumors are usually an incidental finding on a chest radiograph. These tumors have a characteristic radiographic appearance: a distinct round, oval, or biconvex lenslike appearance, with sharp margins that merge with the interlobar fissure. A pseudotumor in the oblique fissure is most apparent on lateral views, in which it appears as a spindle-shaped opacity within the plane of the fissure.^7-9

Pulmonary pseudotumors can easily be misinterpreted as lung nodules or masses. The differential diagnosis includes transudates, exudates, hemothorax, and chylothorax. A correct diagnosis of pulmonary pseudotumor can avoid an invasive and expensive workup for pulmonary malignancy.

A pulmonary pseudotumor should be suspected whenever radiographic densities with typical features are seen in a patient with fluid overload secondary to renal or heart failure. The diagnosis is established when the follow-up chest radiograph reveals resolution of lesions after treatment of the underlying cause.¹⁰ In some cases, a CT scan of the chest may be necessary for a definitive diagnosis.

Outcome in this case

The pulmonary pseudotumor in this patient resolved with diuresis and dialysis over 1 week. The patient was subsequently discharged and was scheduled to receive outpatient hemodialysis for end-stage renal disease.

References:

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