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This excerpt is from the Sept 2019 version of their vasectomy page:
A thorough preoperative discussion of the procedure by the clinician performing the vasectomy is equally important, as is true for any surgical procedure, and should review the risks, complications, and long-term effects associated with vasectomy. However, the American Urological Association (AUA) guidelines for vasectomy state that clinicians do not need to routinely discuss coronary heart disease, stroke, dementia, hypertension, prostate cancer, or testicular cancer in pre-vasectomy counseling of patients because vasectomy is not a risk factor for such conditions.
Sperm granuloma — Sperm are highly antigenic and stimulate a significant inflammatory reaction. A sperm granuloma may form when sperm leaks from the testicular side of an open-ended vas following vasectomy. Less commonly, they may form with extravasation from a cauterized or fulgurated vas.
These granulomas are rarely symptomatic and may be protective to the testis and epididymis. The granuloma is rich in epithelial-lined channels that may vent leaking sperm away from the epididymis and protect against increased intraepididymal pressure.
Most granulomas are asymptomatic and over time will ultimately resorb. Granulomas, however, have been implicated in increased rates of post-vasectomy pain and in vas recanalization related to the inflammatory response induced by the antigenic reaction to sperm Link. Patients with an acute symptomatic granuloma typically present two to three weeks after vasectomy, after they have resumed sexual activities. A tender mass can be palpated near the cut testicular end of the vas. Most patients respond to supportive care including nonsteroidal anti-inflammatory drugs (NSAIDs); surgery is rarely needed.
Epididymitis — Congestive epididymitis can occur at any time after vasectomy. The open-ended technique may in theory reduce that risk.
Post-vasectomy pain syndrome — Post-vasectomy pain syndrome is distinct from postprocedure pain; however, there is some controversy regarding its definition and therefore prevalence (Link). Historically, rates for post-vasectomy pain syndrome have been reported as very low (<1 percent). However, surveys have found that the incidence of “troublesome” post-vasectomy pain is reported by approximately 15 percent of men, with pain severe enough to impact quality of life in 2 percent; survey respondents, however, may not have been representative of all post-vasectomy men (Link 1) (Link 2) (Link 3) (Link 4).
The cause of most post-vasectomy pain syndromes is chronic congestive epididymitis (Link). Testicular fluid and sperm production remain constant following vasectomy. The majority of this fluid accumulates in the epididymis, which then swells. While asymptomatic in most men, some will develop a chronic dull ache in the testes, which is made worse by ejaculation. Other causes or contributors to pain syndromes include the formation of sperm granuloma, or nerve entrapment at the vasectomy site.
First-line therapy for post-vasectomy pain is the administration of nonsteroidal anti-inflammatory medications and warm baths. If unsuccessful, local nerve blocks or steroid injections may be performed by a pain specialist. If the post-vasectomy patient’s discomfort is localized to a tender, palpable granuloma, this may be excised, followed by fulguration of the leaking end of the vas Link.
Refractory cases may require surgery, including either vasectomy reversal (vasovasostomy) or complete epididymectomy. Vasovasostomy successfully relieves pain in up to 70 to 82 percent of well-selected patients (Link 1) (Link 2). These patients, however, will almost always require the use of another form of contraception as a result.
Complete epididymal resection is reserved for the most severe cases. Injury to the testicular blood supply, a known complication of this procedure, causes testicular atrophy. Thirty to 90 percent of patients undergoing epididymectomy for post-vasectomy orchialgia will have residual scrotal pain (Link).
Kidney stones — An association has been found between vasectomy and increased risk for kidney stones (Link 1) (Link 2). A case-control study found a twofold risk for kidney stones in men younger than age 46 (RR 1.9, 95% CI 1.2-3.1) but not for men aged 46 years or older (Link 1). The physiologic mechanism for this increased risk is unknown.
UpToDate says that studies have not shown that vasectomy causes any cardiovascular disease, testicular cancer, immune dysfunction (asthma, diabetes mellitus, thyrotoxicosis, multiple sclerosis, myasthenia gravis, inflammatory bowel disease, testicular atrophy, ankylosing spondylitis, or rheumatoid arthritis). UpToDate reports the link to prostate cancer as controversial, and no causative link has been proven.