Brief Answer:
Several factors to be considered...

Detailed Answer:
Hello and Welcome to 'Ask A Doctor' service...
I've gone through your query in details...
I can understand your concern...

Well, please note when it's the size of a small egg, it could be anywhere from a lipoma (a benign mass) to any other form of lump (not necessarily a cyst which in fact are quite smaller in size)...

The first thing to consider in that scenario is the symptoms...if it's not giving any bothersome symptoms, no headaches, pain, heaviness of head etc, not increasing in size then better to leave it alone (considering it's been 5 years already)...

However, for detailed evaluation, ideally, it should be investigated further (an MRI of the brain and the adjoining neck should be performed at first to see the extent of the lump inside)...based on the findings, a further decision regarding surgery can be taken...

No, not a Dermatologist, if no extent inside the brain was found, then it can be simply removed by an experienced General Surgeon...In case there's any extension found inside the brain then a Neurosurgeon would be the right one to remove it surgically...

Duration of surgery entirely depends on the extent of the lump, surgical expertise of the operating surgeon, the operating set-up, your pre-op and intra-operative health conditions (in general, it can be anywhere from 1hour to 3-4hours)...

Scar-mark again is entirely dependant on those previous factors only, however, if it's inside the hairline, then chances of hair regrowth afterwards are quite likely, so not to worry...

Hope this answers your queries...
Let me know if I can assist you further.

Take Care
Kind Regards

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