My lymphoma is in my mediastinum so I was supposed to have a mediastinoscopy (for my biopsy). I'd say it's more on the minor side relative to the other surgeries a cardiac surgeon does. However it's not so minor that it's outpatient. They planned to have me stay 1-2 nights in the hospital.
Anyway I didn't end up having the mediastinoscopy. My cardiac surgeon decided to do a Chamberlain (modified/mini thoracotomy) instead. Best of luck to you.