Hi.. Thanks for asking us...
I can understand your situation.. It makes you feel weird when you find such indentation in skull.. Its rare symptom to have..
In this situation i can see few possibilities
-sometimes
vitamin A toxicities can lead to this.. check if you are taking any supplements with overdose
-As you mentioned lump in neck it gives possibility of two things
1.Some thyroid cancers can cause seeds in bone specially skull leading to
bone damage .. but usually they present with pulasatile swellings..but we
cant rule it out completely without investigations
2.
Parathyroid problem causing disturbance of clacium and bone metabolism
-Finally a rare thing Gorhams disease where bone replaced by vessels causing indentation...
All these things need thorough investigations.. so please let your physician know this skull bone indentation when you meet.. i advise you to consult surgeon or
endocrinologist for this situation..
Hope your situation will be solved soon...