A 42-year-old man presents to his doctor with complaints of left-sided flank pain radiating into his groin. The pain began suddenly and has increased in intensity. He had a similar problem several years ago, but he did not seek medical attention, and his symptoms resolved spontaneously. He denies fever, chills, nausea, or vomiting. He has had no diarrhea or difficulty urinating. Physical examination is remarkable for tenderness along the left flank and into the groin, but is otherwise normal. There are no inguinal hernias detected on examination. A urinalysis reveals microscopic hematuria without casts. Serum chemistry reveals: Sodium: 143 mEq/L Potassium: 2.4 mEq/L Bicarbonate: 17 mEq/L Chloride: 115 mEq/L Blood urea nitrogen: 12 mg/dL Creatinine: 1.0 mg/dL Glucose: 85 mg/dL Which of the following is MOST likely present in this patient?