Ok, this isn't really a 四字熟語 in the classical sense, but I like it, so bear with me. I recently started law school, and this seems particularly fitting for how I've spent my last week or so.
Setting aside the irony of the fact that I am posting now that I actually have other things to do, and barely made any updates during my 2-month period of unemployment, this particular phrase deals with someone who is so busy with studying that they never leave their house.
1) "Professor Shut-in"
The big difference between myself and actual 閉戸先生's, of course, is that they actually study out of intellectual curiosity, whereas I study... because I have to (at least, that's what I tell the cool kids).
My first thought when I heard this was of the monk who was so passionate about memorizing scripture he sat at his station until his legs decayed below him. My legs feel asleep way too quickly for me to make it quite that far, but studying has had something of an effect on my social life (coupled with the tropical storm that passed through yesterday, I didn't leave my apartment for something like 36 straight hours this weekend).
Back to the Japanese, being a 閉戸先生 isn't really a good thing; the fact that your door is closed (the 閉戸 part) means that you are ignoring your neighbors, and by extension your human relationships. You're not necessarily a social outcast, but you are more cut off than you should be. As we saw with Jeff's recent explication of the word 縁, human relationships are not something to be taken lightly, so make sure you never go to la... I mean, never become a 閉戸先生.
Professor X is a talented scholar, but he's something of a bookworm and has problems getting along with people.
Don't ever put "bookworm" into google image search at work, at school, or in the presence of children or easily offended people. Take it from someone with experience.