The anatomy of pelvic pain perception
Convergence of sensation
Somatic pain. Painful impulses originating in the skin, muscles, bones, joints, and parietal peritoneum travel in somatic nerve fibers.
Visceral pain. Painful impulses originating in the internal organs travel in visceral nerves.
Visceral pain is more diffusely localized than somatic pain and has a less well-defined area of projection to the sensory cortex of the brain for its identification. Also, there are many more somatic neurons than viscerosomatic ones in the dorsal horn of the spinal cord.
These differences result in a convergence of sensation that may be difficult for the patient and physician to interpret. Visceral pain is usually interpreted as coming from the skin and other surface tissues, which are supplied by the corresponding spinal cord segment, resulting in referred pain. For example, the initial pain of appendicitis is perceived to be in the epigastric area, because both are innervated by the thoracic cord segments T8, T9, and T10.
Since innervation of the lower intestinal tract is the same as that of the uterus and fallopian tubes, patients may experience pain caused by GI pathology as gynecologic pain.
Pain sensitivity of genital tissues
- External genitalia are exquisitely sensitive.
- Vaginal pain sensation is variable.
- The cervix is relatively insensitive to small biopsies but is sensitive to deep incision or to dilatation.
- The uterus is very sensitive.
- The ovaries are insensitive to many stimuli, but they are sensitive to rapid distension of the ovarian capsule and compression during physical examination.
Reproduce the pain on physical examination
Examination should be conducted in a way that does not provoke involuntary guarding, which may obscure findings. Gaining trust beforehand is important, as is taking time to explain what will be done during the exam.
Ask the patient to show you where the pain occurs, if possible, and try to reproduce the pain by palpation. Look for abdominal distension, and locate any tender areas. Continue the pelvic examination in this way, always attempting to reproduce and localize the pain. Look for any tenderness, nodularity (especially in the cul-de-sac), and palpable masses in the cul-de-sac or adnexal regions.
Examine the abdominal wall for evidence of myofascial trigger points and for iliohypogastric (T12, L1), ilioinguinal (T12, L1), or genitofemoral (L1, L2) nerve entrapment. Then ask the patient to tense the abdominal muscles by performing a straight-leg–raising maneuver or a partial sit-up. Points that are still tender, more tender, or that reproduce the patient’s pain after these maneuvers should be injected with 2 to 3 mL of 2.5% bupivacaine. Chronic abdominal wall pain is confirmed if the pain level is reduced by at least 50%.
Chronic low back pain without abdominal pain is seldom of gynecologic origin. If there is evidence of musculoskeletal disease, consider consulting an orthopedist. Neuromuscular symptoms may be accompanied by a pelvic mass. Positive neurologic signs such as muscle weakness or abnormal reflexes should prompt consultation. In such cases, surgical exploration may reveal a neuroma or bony tumor.
Lab, imaging studies: How useful?
Traditional laboratory studies are of limited value, although a complete blood cell count, erythrocyte sedimentation rate (ESR), and urinalysis should be obtained. The ESR is nonspecific and will be elevated in any type of inflammatory condition, such as subacute salpingo-oophoritis, tuberculosis, or inflammatory bowel disease.
A thorough genitourinary evaluation is important, including cystoscopy when suspicion of urinary tract disease is high. If no obvious cause for the pain is uncovered, pelvic ultrasonography may be helpful. This is especially true in an obese or uncooperative patient, when bimanual pelvic examination is difficult.
If bowel or urinary signs and symptoms are present, then an endoscopy, abdominal and pelvic computed tomography, cystoscopy, or computed tomography urogram may be useful.
No diagnosis, no reason for surgery? Start therapy for endometriosis
If the workup yields no diagnosis and rules out indications for surgery, such as significant adnexal mass, then empiric medical therapy for endometriosis is appropriate without laparoscopic confirmation.1
Begin a trial of empiric therapy with a nonsteroidal anti-inflammatory drug such as ibuprofen or naproxen, oral contraceptives, or both.1 Women with ovarian pathology (eg, periovarian adhesions, recurrent functional cyst formation) and those whose pain worsens midcycle, premenstrually, or menstrually may experience improvement with a trial of oral contraceptives to suppress ovulation and menstruation.
Use second-line empiric therapy before diagnostic laparoscopy
If these treatments fail, begin empiric therapy with second-line agents such as danazol, progestins, or gonadotropin-releasing hormone (GnRH) agonists. Laparoscopic confirmation is unnecessary.
Several publications, including a 2002 consensus statement on management of chronic pelvic pain and endometriosis, support this approach.1,3-5 In fact, following recent guidelines for evaluating and treating CPP is likely to lead to fewer invasive procedures for diagnosis and treatment, including laparoscopy and hysterectomy.