Syndrome of Inappropriate Antidiuresis Due to Chronic Perforated Diverticulitis With Colovesical Fistula

A 54-year-old man presented with symptoms of dysuria and cloudy urine, as well as a history of passing stool in urine and repeated urinary tract infections over the past three months. He had previously undergone surgery for diverticulitis with secondary peritonitis 22 years prior. At the time of examination, the patient was in good general condition and euvolemic and had a plasma sodium level of 128 mmol/L and abnormally elevated urinary osmolality. Treatment involved oral urea and drinking according to thirst. After ruling out hypothyroidism and secondary adrenal insufficiency, the patient was diagnosed with syndrome of inappropriate antidiuresis (SIAD). A neoplastic-like mass in the sigmoid colon that infiltrated the bladder floor with a fistulous tract was found. The patient underwent a planned surgical intervention and maintained eunatremia without urea treatment postoperatively. The biopsy showed diverticulosis with intense inflammation in the submucosa but no neoplasia. This is the first reported case of SIAD associated with a colovesical fistula due to chronic perforated diverticulitis.