Rarer forms of cervical esophageal diverticula are the Killian's diverticulum and the Laimer's diverticulum. This includes diverticula becoming inflamed (diverticulitis) or bleeding. Congenital urethral diverticula can arise from several embryological sources. The diagnosis of acute diverticulitis is made confidently when the involved segment contains diverticula. Acquired urethral diverticula can be caused by trauma and/or infection. Urinary retention can lead to bladder diverticula, kidney stones, and reflux nephropathy. Histopathologically, several characteristics are frequently visible in urethral diverticula. Sometimes, inflamed diverticula can cause narrowing of the bowel, leading to an obstruction. Few urethral diverticula are present at birth; the vast majority are acquired. A pair of simple or branched diverticula are connected to the rectum. These postulated diverticula would have taken the form of inflatable soft-tissue sacs. These contain an outpocketing of digestive gland called the diverticula. Diverticulosis (the presence of bowel diverticula) is an essentially ubiquitous phenomenon. Each opens in a vas deferens which bears three diverticula or "vesiculae seminales". Large-mouth diverticula are associated with scleroderma.