Sciatic nerve endometriosis is widely considered a rare occurrence, but leg pain in patients with endo is relatively common, up to 50%. Why? Is it being underdiagnosed? Since endometriosis itself is often misdiagnosed or diagnosed years after initial symptoms, the true incidence of direct and indirect sciatic nerve symptoms caused by endo is also suspect.
The sciatic nerve is located very deep within the pelvis but not inside the intraperitoneal area where the uterus is situated. Instead, the sciatic nerve is found in the “retroperitoneum,” the deep anatomic region behind the peritoneum, containing bones, muscles, and major nerves. It exits the pelvis right behind the Piriformis muscle, which is part of the pelvic floor.
Endometriosis mainly involves intraperitoneal pelvic structures and organs such as the bladder, cul-de-sac, large and small bowel sections, uterus, ovaries, and Fallopian tubes. In advanced cases, it can extend into the midline retroperitoneum by involving the recto-vaginal septum. However, endometriosis has been identified in atypical and distant locations by unclear means of spread, and a certain percentage is deeply infiltrating. In the latter case, the retroperitoneum, sciatic nerve, and pelvic floor muscles are anatomically very close and vulnerable to direct deep infiltration or indirect spread (e.g., lymphatic system). The precise prevalence of endometriosis that grows outside the pelvic intraperitoneal cavity by location, including the sciatic nerve area, remains to be discovered due to the limited number of published studies on the subject.
Symptoms:
Lower back, leg, and buttock pain, which may or may not extend down your leg, may indicate the presence of direct sciatic endometriosis or indirect inflammation-related pressure on the nerve. The symptoms may be the same or very similar since the endometriosis is either directly growing and pressing on or involving the sciatic nerve or leading to pelvic floor inflammation and scarring, which also affect the sciatic (and other nerves) and trigger pain signals. The latter is typically called Piriformis syndrome.
Sciatic endometriosis may or may not be uncommon. Still, it must always be included in the “differential diagnosis” (identifying root causes of symptoms) of pain and signs in the region or area where sciatic nerve sensation fibers are known to extend.
Testing and Diagnosis:
Lab tests are generally not helpful in diagnosing sciatic endometriosis. A CA-125 level (an ovarian cancer tumor marker) or hsCRP (generalized inflammatory marker) can be elevated in endometriosis due to inflammation but are not specific for endometriosis, let alone sciatic nerve involvement.
Arguably the best imaging study for possible endo-related extraspinal sciatica is the MRI. It may reveal whether an endo lesion is directly growing in or around the nerve, most frequently at the sciatic notch, or compressing it, such as inflammation causing Piriformis syndrome. However, unless endometriosis has already been confirmed from prior surgery, these scans will only sometimes help diagnose endo or endometriosis-related sciatica. But the running message is this. Given the diagnostic uncertainty of endometriosis, extra pelvic symptoms should never be dismissed as unrelated when an endo diagnosis is being considered.
Symptoms and Findings:
Pain may or may not be cyclical, similar to rectal pain caused by endometriosis. It may start before menstruation and persist for several days after a period has ended. The pain may be accompanied by motor deficits (weakness or gait/walking issues), foot drop, and discomfort or tingling radiating down the back of the leg from the buttock. Walking, especially long distances, may exacerbate these symptoms. Deep buttock tenderness may also be present, specifically in the area of the sciatic notch where the sciatic nerve passes. If left untreated, sciatic endometriosis may lead to long-term nerve damage, as any prolonged direct pressure or inflammation around a major nerve can cause this.
A doctor or pelvic floor therapist may identify “deficits” (abnormalities) in the sciatic nerve distribution during a physical examination. For example, Lasègue’s test, which is a straight leg raise test when lying on your back, may point to sciatic involvement by endo. Localized deep tenderness over the sciatic notch might also be present, although it can be difficult to reproduce. On the other hand, a regular pelvic exam may be normal, depending on the extent of endometriosis in the pelvis.
Treatment of Sciatic Endometriosis:
The treatment of sciatic endometriosis will most likely begin with surgery. In fact, it may be the only definitive treatment. But this is not always the case. Endometriosis excision of an endometriosis lesion in this area is the gold standard, just as in other areas. But if direct sciatic involvement by endo is suspected, choosing the right surgeons is especially crucial. The sciatic nerve is located so deep within the pelvis that a general gynecologist most likely has never encountered it during surgery. Endo-excision surgeons do not typically operate in this retroperitoneal area either. Gynecologic oncologists, who often work on lymph nodes or remove cancer in the region, are more likely to be familiar with the anatomy. However, if the nerve is more likely to be directly affected by endo based on imaging, a neurosurgeon should also be part of the team. Therefore, a gynecologic oncologist and/or an endo excision surgeon very experienced in advanced endo and a neurosurgeon are likely the best options for this aspect of endometriosis excision surgery.
Given that some percentage of endo-related sciatica may be due to pelvic floor inflammation and dysfunction, as opposed to direct endo growth on or near the nerve, pelvic floor physical therapy is worth trying first. If it is effective and if imaging does not show evidence of deep infiltrating endo that might be directly involving the sciatic nerve, then radical and more risky retroperitoneal surgery to get to that area may be safely deferred.
In cases where direct involvement is suspected and surgery is not immediately feasible, a short-term medical treatment regimen with anti-inflammatory and possibly anti-estrogenic properties may be beneficial. Adopting an anti-inflammatory diet may also help. Pelvic floor physical therapy and medical support therapy, including vaginal Valium, may offer additional temporary benefits. The bottom line is that treatment for pain along sciatic nerve distribution should be tailored to each individual’s needs and integrated into a comprehensive, personalized medical-surgical treatment plan.
The first confirmed case of sciatic endometriosis was reported in 1946 by Schlicke. The primary takeaway from this fact is that sciatic endometriosis has been a known entity for over half a century. Since then, other cases have been documented in medical journals. However, overall, it is still considered a rare condition. But given the percentage of endo patients who report leg pain, this may not be so, especially when endo-induced Piriformis syndrome is added to the mix. If endometriosis has already been diagnosed or strongly suspected and sciatic nerve distribution pain is part of the symptoms, a consultation with an expert who focuses on advanced endometriosis patients may save you a lot of grief.
References:
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