I went to see a 31-year-old man who was complaining of headaches and a bump on his scalp just above the forehead. The bump on his scalp was unusual. It was red and tender. It looked and felt kind of like an abscess though it is unusual for someone to develop an abscess on that part of the scalp.
A good way to find out if a bump in the skin is an abscess is to poke a needle into it and aspirate with a syringe to see if any pus comes out. I recommended this to the patient and he agreed.
I got a needle and syringe then wiped the bump with an alcohol swab. I poked the needle into the skin over the bump and pulled back on the plunger. I then slowly advanced the needle, watching for pus. I knew if the needle hit the skull and no pus came back in the syringe it was not an abscess.
But, the needle never hit the skull. Just as I realized this, the syringe started to fill up with liquid. It was not the yucky, thick pus I was expecting from an abscess, but clear, colorless liquid. Cerebral spinal fluid. The fluid that bathes and supports the brain inside the skull. I had poked a needle through his skull!
Shaken, I told the patient what happened. I then ordered x-rays, which clearly showed there was no skull under the lump.
I made arrangements for the patient to be watched in the hospital since I had potentially contaminated his cerebral spinal fluid. This put him at risk of an infection around the brain.
As it turned out, he got no infection and was later diagnosed as having an eosinophilic granuloma or Langerhans cell histiocytosis. This rare condition caused the replacement of normal skull tissue with a tumor that caused the bump on his head.