Abstract
Abdominal wall pain, a specific subset of abdominal pain, is often overlooked by healthcare providers. It is estimated that 2% to 3% of patients with an initial complaint of abdominal pain actually have the diagnosis of abdominal wall pain. The most common cause of abdominal wall pain is anterior cutaneous nerve entrapment (ACNES); however, the differential diagnosis can be quite vast. The diagnosis of abdominal wall pain is usually made clinically with an array of physical exam maneuvers. A multidisciplinary approach to treatment can effectively reduce symptoms and improve quality of life, and includes exercise therapy, therapeutic modalities, and interventional injections. A thorough diagnosis is required to adequately treat the patient appropriately.
Keywords
Abdominal Wall, Chronic, Nonvisceral, Pain
| Synonyms | |
| |
| ICD-10 Codes | |
| G 58.0 | Intercostal neuropathy |
| G 58.8 | Other specified mononeuropathies |
| S39.011A | Strain of muscle, fascia and tendon of abdomen; initial encounter |
| S39.011D | Strain of muscle, fascia and tendon of abdomen; subsequent encounter |
| S39.011S | Strain of muscle, fascia and tendon of abdomen; sequelae |
| G89.29 | Other chronic pain |
Definition
Abdominal pain can have a variety of visceral and peripheral etiologies, and abdominal wall pain, a specific subset of this pain complaint, is often overlooked by healthcare providers. One study estimated that 100 patients with abdominal wall pain in a particular population had previously undergone over 400 diagnostic procedures prior to their ultimate diagnosis. This obviously leads to both increased healthcare costs and a delay in treatment.
Pain originating in the abdomen can come from a variety of sources and it is helpful to initially differentiate the patient’s complaints between pain originating from abdominal viscera and pain originating from the abdominal wall itself. It is estimated that 2% to 3% of patients with an initial complaint of abdominal pain actually have the diagnosis of abdominal wall pain and that likelihood increases to 30% in individuals with the diagnosis of chronic abdominal pain with no known pathology. Looking at various studies, this percentage can range from 11% to 30%.
The prevalence of abdominal wall pain in the general population is not known. The most common cause of abdominal wall pain, anterior cutaneous nerve entrapment (ACNES), has been reported to have a 2% prevalence among those patients with abdominal pain.
Although without a known causality, women are four times more likely than men to be affected with abdominal wall pain, and pregnancy and the use of oral contraceptives have been reported to exacerbate abdominal wall pain due to estrogen and progesterone effects on soft tissue edema. Understanding the pathophysiology of abdominal wall pain and the differences between wall pain and visceral pain can help a provider adequately identify and treat this condition.
To understand the diagnosis and treatment strategies, it is important to know the anatomy of the abdominal wall. Starting with the musculature, the abdominal wall is fortified anteriorly by the vertically striated rectus abdominis musculature that is joined centrally by a fibrous layer known as the linea alba. This fibrous layer acts as the aponeurosis of the abdominal musculature. The rectus abdominis is flanked laterally by another layer of fascia known as the linea semilunaris, which is in direct connection to the laterally oriented internal oblique muscles. Superficial to the internal oblique musculature we find the external oblique muscles. Deep to the internal oblique we find the transverse abdominis muscle layer. Major arterial supply to these muscular layers arises from branches of the internal thoracic artery (feeding the superior epigastric artery) and branches of the external iliac artery (feeding the inferior epigastric artery).
The innervation to the abdominal wall originates from intercostal nerves derived from the T7 to T12 nerve roots posteriorly. The intercostal nerves run along the inferior border of their respective rib before reaching the lateral edge of the rectus abdominis muscle. At this point, the nerve takes a 90-degree turn anteriorly and travels from the posterior rectus sheath, through a neurovascular channel in the rectus muscle (adjacent to the linea semilunaris) containing a fibrous ring, then through the anterior sheath, where another 90-degree turn is made to continue along the anterior abdominal wall. Given the tortuous nature of the sensory nerves, there can be multiple areas of entrapment leading to abdominal wall pain. In addition, due to the concept of neural convergence of different visceral and somatic inputs into the spinal cord, there can be referred pain to the abdominal wall from a central visceral source. Lastly, thoracic nerve radicular pain can present as abdominal wall pain and involvement of nerve roots T6 through T12 can manifest as radiating pain originating from the posterior aspect wrapping around to the anterior abdomen ( Fig. 95.1 ).
Symptoms
Patients often complain of localized pain within a specific region of the abdomen. The pain is commonly described as sharp, stabbing, or dull in nature and can easily be located by the patient or examiner. Although there can be a degree of radiation of the dull pain sensation, the patient can oftentimes pinpoint the sharp epicenter of pain with one fingertip; however, in severe cases, the pain can diffusely radiate to a larger area. Although not common, there may also be a degree of hypersensitivity and allodynia. Patients often complain of pain that is constant or fluctuating, rather than episodic (Suleiman et al.); however, they may occasionally go months without the complaint. The most frequent location of this pain is along the lateral edge of the rectus abdominis muscle. In some cases, retrograde proximal radiation of pain from the distal site of nerve entrapment may occur (Valleix phenomenon) and can mimic a thoracic radiculopathy. The pain level does not usually fluctuate with food intake or bowel movements; however, it can be exacerbated by increased strain of the abdominal musculature, during lifting, coughing, laughing, or the Valsalva maneuver. Patients often have difficulty sleeping on the affected side, as the pain often increases with the side-lying position as opposed to lying supine. To this point, abdominal wall pain tends to be positional in nature and temporary relief can be achieved by sitting upright or resting in a slightly flexed supine position.
Compression of the involved abdominal sensory nerves from postoperative scarring or even tight clothing such as belts, corsets, and lumbar braces can also be a cause for this pain complaint. In more serious conditions such as rectus sheath hematoma due to a rectus muscle tear or shearing of the epigastric arteries, pallor, confusion, and hypovolemic shock can occur over time. Rectus sheath hematomas are most often linked to blunt abdominal trauma or anticoagulation therapy.
Physical Examination
The diagnosis of abdominal wall pain is usually made clinically. As mentioned previously, patients can often pinpoint an area of superficial maximum sharp tenderness most often along the lateral edge of the rectus abdominis. Hyperalgesia and hypesthesia have been noted in two thirds of patients, specifically with the diagnosis of anterior cutaneous nerve entrapment. Patients with a large body habitus may make the examination a bit more challenging. The patient is best examined in the supine position with the abdomen exposed. Attention should be given to any rashes or erythema on the superficial surface. Light and deep palpation along the four quadrants of the abdomen can be done at this point.
In some instances, the examiner may be able to palpate the oval shaped aponeurotic openings of the neuromuscular foramina in the rectus abdominis. In general, T6, T7, and T8 are located where their respective ribs intersect the edge of the rectus muscle. T10 is located at the lateral edge of the rectus muscle at the level of the umbilicus. T12 is located somewhat closer to the midline at the level of internal inguinal ring.
Light and deep palpation may add value to the examination; however, the Carnett test is recommended at this point. Carnett test is performed by having the patient lie supine while the practitioner visually localizes the area in question. The patient then tenses the abdominal wall, and the examiner then presses the region. In the case of abdominal wall pain, typically the pain then either remains unchanged or worsens. This is a positive test. In contrast, patients with pain originating in the abdominal viscera have markedly less pain when they tense the abdominal wall muscles. This would be considered a negative Carnett test. The Carnett test is 78% sensitive and 88% specific for the diagnosis of abdominal wall pain.
A subsequent algorithm ( Fig. 95.2 ) has been devised to further interpret the results of Carnett test in different scenarios. If pain is elicited near a surgical scar in the absence of a hernia, then a local anesthetic injection is provided with a positive diagnostic block, resulting in complete relief of the pain. If the pain increases with spinal flexion, extension, or rotation, then thoracic radiculopathy is suspected. If movement of this nature does not reproduce the pain, then attention is returned to the abdominal wall where the diagnoses of myofascial pain, ACNES, or even hematoma are investigated. Depending on the location of the pain, one can then look into specific causes of pain. Using the algorithm may be beneficial, as it was measured to have a sensitivity of 85% and a specificity of 97% as compared to the Carnett test alone, which proved to have a sensitivity of 78% and a specificity of 88%.
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