A 50-year-old man presents to the office for evaluation of persistent perianal pain and pressure. He reports it started approximately 4 days ago, and has worsened. He reports he has avoided defecation because of the discomfort. Vital are as follows: T 101.2F, BP 140/80 mmHg, HR 88 bpm, RR 16/min, SpO2 99% on room air. Physical exam reveals an area of fluctuance measuring approximately 4cm in diameter in the right perianal region with swelling of the perirectal tissue on the right. Digital rectal exam reveals significant tenderness in the area of the induration, but normal rectal tone or gross blood. What is the most likely diagnosi