Sources close to the Delaware attorney general and older son of vice president Joe Biden say a biopsy will determine if the mass is cancerous. Results are expected to take several days.
Joined by his father and wife, Hallie, the 44-year-old arrived in Houston on Monday following a recent spell of weakness and disorientation during a family vacation in Indiana. Last week, he visited hospitals in both Chicago and Philadelphia before deciding to make his way to the Texas Medical Center.
The younger Biden suffered a mild stroke in May 2010, spending a week in the hospital and a month at home recuperating.
Medical records released during the 2008 presidential election revealed that Joe Biden received treatment for two brain aneurysms at Walter Reed Hospital in 1988, when he was a 45-year-old U.S. senator.
As of Wednesday, NBC News confirms that the vice president remains in Houston.