CT checks PET false positives in esophagus

When it comes to detecting primary and metastatic disease in patients with esophageal squamous cell carcinoma, it's best to back up PET scans with CT data. Chronic inflammatory diseases could inflate PET's false-positive results, according to a study from Korea.

Researchers evaluated 81 patients who underwent separate FDG-PET and CT studies before esophagectomy and lymph node dissection. They found PET less specific but more sensitive than CT for depicting nodal metastases. PET's high sensitivity came at the expense of a high false-positive rate.

Approximately 98.2% of the false-positive results corresponded to thoracic lymph node groups. More than half - 32 nodal groups in 20 patients - were for hilar node groups. The study was published in the June issue of Radiology.

"When interpreting hilar nodes on PET in patients with squamous esophageal cancer, you should be cautious," said coauthor Dr. Kyung Soo Lee, a radiologist at the Sungkyunkwan University School of Medicine's Samsung Medical Center in Seoul.

Since granulomatous disease is endemic in Korea, researchers attributed the high number of false-positive results on PET to the presence of reactive hyperplasia or active inflammation of normal-sized lymph nodes.

Physicians performing PET studies in areas of endemic chronic inflammatory diseases, such as tuberculosis and bronchiectasis, should tailor their interpretation, Lee said. Coincidentally, squamous cell carcinoma of the esophagus is more widespread in TB-endemic areas.

When calcified nodes of more than 60 HU on unenhanced images show increased FDG uptake, they're probably benign and signify a granulomatous inflammation, he said.

Endoscopy, the standard of care to evaluate the primary tumor, has a questionable accuracy for lymph node evaluation. Combined thoracoscopy and laparoscopy have excellent accuracy rates for detection of regional and distant metastases, but they are highly invasive.

Hybrid or coregistered PET/CT images may provide an option for accurate detection and staging of esophageal squamous cell carcinoma. Calcified lymph nodes detected on CT, for instance, may also show increased FDG uptake, reducing the likelihood of false-positive readings, Lee said.

"Coregistration may help enhance the diagnostic accuracy by presuming that the calcified nodes showing increased uptake are benign," Lee said.

For more information from the Diagnostic Imaging archives:

PET/CT begins to make a clinical difference
http://www.dimag.com/db_area/archives/2003/0308.cover.di.shtml

Barium studies rule out esophageal carcinoma
http://www.dimag.com/db_area/archives/europe/2003/0306.imagingnews4.die.shtml

Esophageal cancer staging benefits from PET, US, CT combo
http://www.dimag.com/db_area/onlinenews/2002/2002061802.shtml?ref=log