"Pink spots" in formalin-fixed brains--poor fixation or bacterial byproduct?

Circumscribed pink areas 0.3-1.0 cm in diameter seen in deeper parts of otherwise well-fixed brains are usually ascribed to inadequate fixation. Twenty-three patients with pink areas in their fixed brains had evidence of inflammation in at least one organ. Blood vessels in the pink areas contained bacteria. Postmortem cultures identified the organisms in 16 cases. Gram-negative bacteria were the most common. Sharply delineated pink areas in well-fixed brains correlate with postmortem intravascular growth of bacteria.