Rectus sheath hematoma is a relatively uncommon entity that is most often associated with abdominal wall trauma or anticoagulation. Although it is a well-documented condition, its diagnosis can be difficult given its propensity to mimic a variety of intra-abdominal pathologies.
Rectus sheath hematoma occurs as a result of injury to an epigastric artery or its perforating branches within the rectus muscle. Recall that the blood supply to the rectus abdominis muscles originates from the superior and inferior epigastric arteries. The superior epigastric artery arises from the internal thoracic artery and travels caudally within the rectus sheath to anastomose with the inferior epigastric artery. The inferior epigastric artery, deriving from the external iliac, travels cephalad along the posterior surface of the rectus muscle where it lacks the protection of a posterior rectus sheath until it reaches the arcuate line. The arcuate line is located a third the distance between the umbilicus and the pubic symphisis. 
Overall, rectus sheath hematoma accounts for only about 1% to 2% of all causes of acute abdominal pain.  In a 2016 review by Sheth et al. evaluating a series of patients with rectus sheath hematoma, women were more likely than men to develop a rectus sheath hematoma, with a ratio of 1.7 to 1. This is consistent with epidemiologic data demonstrated in other studies. The mean age of patients in Sheth’s review was 67 years. The overall mortality rate associated with rectus sheath hematoma is less than 2% in the most recent publications. 
A few well-documented risk factors are associated with rectus sheath hematoma development. The greatest risk is in those who are therapeutically anticoagulated. In Sheth’s review, almost 70% of patients were on some form of anticoagulation. Naturally, as the prevalence of chemical anticoagulation increases, one may reason that the incidence of rectus sheath hematoma also rises. However, there is a paucity of data in the modern literature to reflect this. In the same series, nearly 60% of patients with rectus sheath hematoma also had chronic kidney disease stage III or greater. Other risk factors, in order of descending prevalence, include abdominal wall injections, steroid or immunosuppressant therapy, cough, femoral puncture, and antiplatelet therapy. 
Epigastric artery rupture can occur when there is direct abdominal trauma or excessively forceful contraction of the abdominal wall. The resulting hematoma may present differently depending on whether it arises in the upper or lower abdomen. When the superior epigastric artery is injured, the resulting hematoma is typically smaller and quickly tamponaded within the rectus sheath. On the other hand, rupture of the inferior epigastric artery is not as easily controlled, owing to the lack of posterior sheath. This allows the development of a larger and generally more clinically significant hematoma. 
In a large case series of 126 patients with rectus sheath hematoma, Cherry et al. report that the most common presenting symptoms are abdominal pain (84%) and a palpable abdominal wall mass (63%).  The character of the abdominal pain varies but is often described as acute in onset, sharp, severe, persistent, and worse with activity. The Carnett sign, first described in the 1920s, is positive if there is an exacerbation of the pain with flexion of the abdominal wall muscles. This indicates the origin of the pain likely is the abdominal wall rather than an intra-abdominal source. The Fothergill sign refers to a palpable abdominal mass that does not cross the midline and remains palpable with abdominal wall flexion, indicating rectus sheath hematoma.  Approximately 55% of patients demonstrate a decrease in hemoglobin of at least 0.4 g/dL from their baseline. Other signs and symptoms are less common but include abdominal wall ecchymosis (17%), tachycardia (13%), hypotension (7.9%), and syncope (1.6%). As mentioned above, the patient may even be peritoneal (9.5%) if the hematoma extends posteriorly and encroaches upon the peritoneum below the arcuate line. 
According to the widely accepted classification of hemorrhagic shock, patients generally do not manifest any hemodynamic changes associated with hemorrhage until at least 15% to 30% of blood volume is lost. While this certainly is a possibility in the setting of rectus sheath hematoma, it is the case in only about 1% to 13% of patients.  Thus the absence of these changes, such as tachycardia, hypotension, or orthostasis, should not lessen the clinician’s suspicion for the diagnosis.
The most valuable laboratory studies for the evaluation of rectus sheath hematoma are hemoglobin/hematocrit and coagulation studies. As previously mentioned, over half of patients would be expected to demonstrate a decline in hemoglobin of greater than or equal to 0.4 g/dL. This is neither sensitive nor specific and thus cannot reliably indicate the presence or severity of a hematoma. However, following the trend of serial hemoglobin values can help establish a trajectory for the patient’s course.
All patients with a suspected rectus sheath hematoma should have baseline coagulation studies at the time of their initial evaluation. Again, a large majority of patients with rectus sheath hematoma are taking some form of therapeutic anticoagulation. For those taking warfarin, the INR can help steer the decision to administer a reversal agent. With the increasing use of antiplatelet therapies and novel oral anticoagulants (NOAC), the INR may be less informative but should still be obtained as part of a coagulation panel.
Ultrasonography of the abdominal wall is a reasonable choice for imaging if needed. Case series have shown it to be around 80% sensitive and specific. However, its reliability is limited by technician skill, body habitus, and patient tolerance. Typical ultrasound findings include a homogeneous fluid collection within the abdominal wall. It may appear heterogeneous, depending on its chronicity and evolution of the hematoma. Ultrasound also allows for serial examination of the size of the hematoma, though this is operator dependent. Doppler color flow does not reliably detect the presence of active extravasation.
CT imaging has been reported to be nearly 100% sensitive and specific for rectus sheath hematoma. Typical CT findings include an often spindle-shaped mass posterior to the rectus abdominis muscle. Its density depends on its chronicity and the use of intravenous contrast. A contrasted study is preferred to detect the presence of active extravasation, though this is not always possible, owing to the prevalence of kindney disease in this patient population. Active extravasation appears as a hyper-dense contrast blush within the mass. There is often accompanying soft tissue edema of the surrounding structures. Though this method of imaging is highly accurate, ultrasound may still be the preferred test in certain circumstances, such as in patients who are pregnant or have kidney disease. 
Fortunately, the majority of cases of rectus sheath hematoma can be successfully managed nonoperatively. Multiple case series have demonstrated that around 80% of patients may be managed with no invasive intervention, including rest, ice, compression, and analgesia.  In patients with coagulopathy, cessation of anticoagulation therapy or if needed reversal of the coagulopathy is sufficient to allow the bleeding to tamponade within the sheath. In patients with significant anemia or hemodynamic instability, transfusion of blood products is indicated. If despite these measures, the patient has persistent evidence of bleeding, the most appropriate initial intervention is angioembolization, which has been reported to control ongoing hemorrhage in virtually 100% of cases successfully.  It is rare for rectus sheath hematoma to require surgical intervention, and in fact, laparotomy in many cases would pose a bigger risk of bleeding to the patient than is necessary, especially in patients with coagulopathy.
Because rectus sheath hematoma is a relatively uncommon entity with a broadly variable presentation, other etiologies of abdominal pain also must be considered in the clinician’s differential diagnosis. Depending on the location of the patient’s pain, the differential may include, among others, appendicitis, diverticulitis, biliary colic, urinary tract infection, tumor and hernia.
The majority of patients recover well with no complications as the hematoma is reabsorbed in 2 to 3 months.  In those with an indication for therapeutic anticoagulation, patients should be counseled on the risk for recurrence with the resumption of therapy.
A rectus sheath hematoma is often difficult to diagnose and its management can be difficult. The condition is best managed by an interprofessional team that includes the emergency department physician, physician assistant, nurse practitioner, radiologist, and a surgeon. Once diagnosed, the majority of patients are treated conservatively with supportive care. A few patients may require surgery or arterial embolization to stop active bleeding.
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