This unfortunate individual was a chronic schizophrenic. Presumably, what began as a scalp scab became deeper and eventually resulted in osteomyelitis through which we was able to insert these foreign bodies. I am not aware of what specific delusions or co-morbidities they had.
The critical learning point, in this case, is that foreign bodies can be tricky to identify if you are not open to the possibility of their presence. The initial CT, performed elsewhere, was reported as "surgical tracks" and "locules of gas" only, with no mention of foreign bodies as there was no plausible history for this.
Had these foreign bodies been left in situ they would have acted as a reservoir for repeated infection.