According to the Mayo Clinic, edema is swelling caused by excess fluid trapped in the body's tissues.
The team said that Howard will be evaluated further in the next few days. Howard has missed the last two games, victories over the Los Angeles Lakers and Dallas Mavericks, because of a sprained right ankle.
On Thursday, Yahoo Sports' Adrian Wojnarowski reported that Howard will get a second opinion on his knee and could miss "extended time."
Howard missed 11 games earlier this season because of a strain in his right knee.
Howard is averaging 16.3 points, 11 rebounds and 1.4 blocks in 32 games this season for the Rockets (32-14), which have won three games in a row and are fifth place in the Western Conference.
- Scooby Axson