AJR: Scintigraphy outperforms CTPA in diagnosing PE during pregnancy

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Lung scintigraphy is more reliable than CT pulmonary angiography (CTPA) in identifying or excluding pulmonary embolism in pregnant patients, according to a study in the November issue of the American Journal of Roentgenology.

Carole A. Ridge, MD, from the department of radiology at St. Vincent ‘s University Hospital in Dublin, Ireland, and colleagues wrote that pulmonary embolism (PE) is the leading cause of maternal death in pregnancy, making its early diagnosis a necessity. The most common imaging methods used to diagnose PE during pregnancy are CTPA and lung scintigraphy.

The authors examined patients with suspected PE, who had been consecutively referred for either CTPA or lung scintigraphy between July 1, 2006 and April 1, 2008 and using EHRs identified CTPA exams and lung scintigraphy studies performed on pregnant patients.

The authors studied 28 CTPA exams performed on 25 pregnant patients and 25 lung scintigraphic studies performed on 25 pregnant patients. They found that ten nondiagnostic CTPA exams were performed on eight patients  (35.7 percent) and one nondiagnostic lung scintigraphic study was performed (4 percent).

According to the authors, the reasons for the diagnostic inadequacy of the 10 CTPA exams included transient interruption of contrast material by unopacified blood from the inferior vena cava (IVC) in eight studies, a missed bolus in one exam, and poor subsegmental opacification in one study. The one nondiagnostic lung scintigraphy study was performed on a patient with a history of smoking and was inadequate for diagnosis because of multiple small predominantly matched abnormalities of ventilation and perfusion.

As far as final diagnosis, in the nondiagnostic CTPA group, one patient had lobar pneumonia and one had PE diagnosed with lung scintigraphy. PE was excluded from the other six patients after further imaging or clinical follow-up exam. In the diagnostic CTPA group no cases of PE were reported. In the diagnostic scintigraphy group, 22 patients had normal studies, two were diagnosed with PE, and the one patient who had a nondiagnostic lung scintigraphic study underwent a CTPA, the results of which were normal.

According to the authors, their comparison of the performance of lung scintigraphy with that of CTPA during pregrancy compared favorably with previous studies. They concluded that lung scintigraphy is the more reliable imaging technique for the diagnosis or exclusion of PE than CTPA because of the interruption of contrast material by unopacified blood from the IVC during CTPA.

“Lung scintigraphy should therefore be considered the technique of choice for imaging of pregnant patients with suspected PE,” the authors wrote, “unless the image quality of CTPA can be optimized with adapted breathing maneuvers and contrast administration."