Rectus sheath hematoma (RSH) (see the image below) is an uncommon and often clinically misdiagnosed cause of abdominal pain. It is the result of bleeding into the rectus sheath from damage to the superior or inferior epigastric arteries or their branches or from a direct tear of the rectus muscle. The emergency physician should be familiar with rectus sheath hematoma because it can mimic almost any abdominal condition. While usually a self-limiting entity, rectus sheath hematoma can cause hypovolemic shock following sufficient expansion, with associated mortality.
See Can't-Miss Gastrointestinal Diagnoses, a Critical Images slideshow, to help diagnose the potentially life-threatening conditions that present with gastrointestinal symptoms.
Rectus sheath hematoma is an ancient disorder first being accurately described by Hippocrates and mentioned by Galen. The first reported case in the United States was by Richardson in 1857.
The best aid to understanding the pathogenesis and making the diagnosis of rectus sheath hematoma is knowledge of the relevant anatomy. The rectus sheath consists of the rectus abdominis muscles, an enveloping fascial sheath, and their blood supply via the epigastric arteries and veins.
The rectus abdominis muscles are two parallel vertically aligned muscles. The rectus abdominis muscles arise from the superior ramus of the pubis and insert into the ventral aspect of the fifth, sixth, and seventh costal cartilages and the xiphoid process. The rectus muscles are separated in the midline by the linea alba. The lateral boundary of the rectus sheath is the linea semilunaris.
The arcuate line is located about 5 cm below the umbilicus and functionally separates the rectus sheath into superior and inferior portions. Above the arcuate line, the aponeuroses of the external oblique, the internal oblique, and the transversalis muscles invest the rectus muscle. Three to four transverse tendinous inscriptions attach the rectus muscle to the enveloping fascia, usually above the arcuate line. The tendinous inscriptions form the typical segmental pattern of the rectus abdominis muscle.
Below the arcuate line, the aponeuroses remain intact anteriorly, but only the weak transversalis fascia and peritoneum separate the muscle mass from the abdominal viscera posteriorly. The inferior retrorectus space communicates with the prevesicular space of Retzius. This communication creates a natural dissection plane between the posterior rectus sheath and the bladder.
The arterial supply to the rectus sheath is derived from the superior and inferior epigastric arteries. The inferior epigastric artery originates from the external iliac artery. It rises from the inguinal ligament to enter the posterior rectus sheath inferiorly. The inferior epigastric artery then ascends loosely between the rectus abdominis muscle and the posterior rectus sheath. During contractions of the rectus abdominis muscle, the length of the muscle changes, and the artery must glide with the muscle to avoid tearing. The combination of the loose attachment of the inferior epigastric artery with the stabilization of its perforating branches fixed to the muscle belly makes the artery prone to shearing stresses at branching sites during strong muscular contraction.
The superior epigastric artery originates from the external thoracic artery. The superior epigastric artery enters the sheath from behind the seventh costal cartilage and descends between the rectus abdominis muscle and the posterior rectus sheath. The superior and inferior epigastric arteries form rich anastomoses near the level of the umbilicus. The anastomoses are microscopic, helping to diminish the likelihood of trauma to the vessels during muscular contraction.
Rectus sheath hematomas (RSHs) are generally caused either by rupture of one of the epigastric arteries or by a muscular tear with shearing of a small vessel. The immediate cause of the rupture may be external trauma to the abdominal wall, iatrogenic trauma from surgery, or excessively vigorous contractions of the rectus muscle. These vigorous contractions are often seen in strenuous exercise or repeated Valsalva maneuvers with severe coughing, vomiting, or straining at the stool. Because the arteries supply the recti posteriorly, most hematomas are posterior to the muscle, making diagnosis by means of palpation more difficult.
Teske's 1946 case series of 100 patients with rectus sheath hematoma showed 60% to be on the right side and more than 80% to be in the lower quadrants.  Right-sided hematomas are presumably more common because more people are right handed and, thus, are more prone to right-sided strain of the rectus muscle during strenuous activity. The lower quadrants are more frequently involved because of the long vascular branches that are present and because muscle excursion during contraction with the absence of the tendinous inscriptions is greater.
Hematomas above the arcuate line are generally caused by damage to the superior epigastric artery or its perforating branches. Patients usually present with unilateral, small, spindle-shaped masses because these hematomas are isolated by the rectus sheath and the tendinous inscriptions, causing tamponade of the bleeding.
Hematomas below the arcuate line are caused by damage to the inferior epigastric artery or its perforating branches. They protrude posteriorly and appear spherical because the rectus abdominis muscle is only supported posteriorly by the transversalis fascia and the parietal peritoneum. Below the arcuate line, hematomas bleed more and may dissect extensively because no posterior sheath wall or tendinous inscriptions are present to tamponade the bleeding. Rectus sheath hematomas below the arcuate line are more likely to cross the midline and become bilobar.
Hematomas near the umbilicus are rare. They are small when they do occur because the microscopic anastomoses of the superior and inferior epigastric arteries near the umbilicus do not allow for significant bleeding.
Hematomas near the peritoneum can result in peritoneal irritation, subsequent abdominal rigidity, and gastrointestinal symptoms. Dissection of the hematoma inferiorly into the prevesicular space of Retzius can masquerade as a pelvic tumor or irritate the bladder, resulting in urinary complications.
In 1996, Berna et al used the appearance of rectus sheath hematomas on CT scans to differentiate 3 levels of severity with disposition and therapeutic implications, as follows  :
Type I: The hematoma is intramuscular, and an increase in the size of the muscle is observed, with an ovoid or fusiform aspect and hyperdense foci or a diffusely increased density. The hematoma is unilateral and does not dissect along the fascial planes. The patient presents with mild-to-moderate abdominal pain and typically does not require hospitalization. Type I hematomas resolve by themselves within 1 month.
Type II: The hematoma is intramuscular (mimicking type I) but with blood between the muscle and the transversalis fascia. It may be unilateral but is usually bilateral, and no blood is observed occupying the prevesical space. A fall in hematocrit may be observed. A patient may require hospitalization for close observation, but most do not require transfusions, and most are discharged to home within 3 days. Type II hematomas usually resolve within 2-4 months.
Type III: The hematoma may or may not affect the muscle, and blood is observed between the transversalis fascia and the muscle, in the peritoneum, and in the prevesical space. A hematocrit effect can be observed, and, on occasion, hemoperitoneum is produced. These patients are often taking anticoagulation medications and require hospitalization. They often require transfusion and are discharged after 1 week. Only rarely will they develop hemodynamic instability that cannot be controlled with fresh frozen plasma and fluid resuscitation. These unstable patients may require surgical intervention. Type III hematomas usually require more than 3 months to resolve.
After resolution, rectus sheath hematomas usually do not recur and typically do not cause long-term sequelae.
Rectus sheath hematoma is an uncommon, but not rare, cause of abdominal pain. In 1999, Klingler et al found an incidence of 1.8% among 1257 patients admitted to the hospital with abdominal pain and undergoing ultrasonography for diagnosis.  Anticoagulation is a well-known risk factor. The incidence is thought to be on the rise, with the increased use of oral anticoagulation drugs and low molecular weight heparins (LMWH).
Although usually a benign self-limiting condition, rectus sheath hematoma (RSH) may be fatal. Mortality figures are prone to error because of the uncommon incidence of rectus sheath hematoma and the paucity of recent mortality data. Overall, the mortality rate is reported to be 4%. The mortality rate for iatrogenic rectus sheath hematoma is reported to be 18%, whereas the mortality rate for patients with rectus sheath hematoma who are undergoing anticoagulation therapy is reported to be 25%. Pregnant patients have a reported mortality rate of 13%, with a 50% mortality rate for the fetus.
These mortality rates were reported prior to the widespread use of ultrasonography and CT scanning to aid in the early diagnosis of rectus sheath hematoma. Early diagnosis likely reduces the mortality rate, but no studies to date are available to demonstrate this.
The high mortality rate in patients undergoing anticoagulant therapy is related to the larger hematomas as well as the increased age and significant comorbidities of these patients.
The morbidity of rectus sheath hematoma is primarily the result of incorrect diagnosis leading to unnecessary exploratory laparotomy, delay in cessation of anticoagulant therapy, or delay in fluid resuscitation and blood transfusion.
As with other abdominal pathology in the older patient, extra care should be devoted to an expedient and accurate diagnosis in elderly patients. Elderly patients are more likely than younger patients to require aggressive resuscitation, anticoagulation reversal, and admission. For these reasons, elderly patients also experience an increased mortality rate.
Rectus sheath hematoma is reported to occur less often in African Americans, with only 4% of rectus sheath hematomas occurring in people of this race. Whether this low rate is physiologic, a result of sample reporting, or diagnostic bias is unknown.
Rectus sheath hematoma is 2-3 times more common in females than in males. The higher incidence in women has been attributed to their decreased muscle mass. The sex distribution seems to be equal in younger age groups, although the predisposing factors differ. Pregnancy is a risk factor in younger females, whereas males more commonly develop rectus sheath hematoma after trauma or muscular exertion.
In a 1946 review of 100 cases, Teske reported the occurrence of rectus sheath hematoma in patients aged 4-83 years, with an average age of 47 years.  The peak age of incidence is in the fifth decade of life. Incidence increases with age as the protection provided by the rectus sheath becomes compromised by decreased muscle mass. The effects of arteriosclerosis and hypertension also render vessels more susceptible to injury.
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