Are anal fistulas minor annoyances or serious medical problems?

No: Fistulas can lead to serious problems if left untreated. The fistula tract may spread, devloping secondary openings with multiple abscesses and draining openings. Long-standing fistulas may develop malignant changes and may be indicative of systemic diseases.

Serious: Source of infection get worse.

Great question: It is RARE for it to heal without surgery but also it is rare for a fistula to threaten one's health. Very rarely we see the infection get into blood stream and make patient very sick and even infect heart valve or infection can get out of control. It is up to the patient as to how much of a bother the symptoms represent. To help decide a patient really should discuss with Colorectal Surgeon