Rectus Sheath Hematoma Workup

• Complete blood cell count: The hematocrit may be normal for small rectus sheath hematomas (RSHs) or significantly depressed with a large hematoma. Serial blood counts may be useful in an expanding hematoma to assess the need for blood transfusion or more aggressive therapeutic measures. The reported white blood cell count ranges from 6.6 X 10³ to 29 X 10³. As in other acute abdominal disorders, a normal white blood cell count does not rule out rectus sheath hematoma.
• Coagulation factors: Although coagulation factors are not helpful for patients on LMWHs, they are useful for patients on oral anticoagulation drugs or for those with a pathologic failure of coagulation. Rectus sheath hematomas are more likely with supratherapeutic anticoagulation, but they can occur in the therapeutic range. Patients undergoing reversal of anticoagulation benefit from serial coagulation factors to assess the response to therapy.
• Arterial or venous blood gas: Knowledge of the base deficit from a blood gas level is useful in patients with hypovolemic shock due to rectus sheath hematoma. Serial blood gas levels can be used to guide fluid resuscitation.

General

When the history and physical examination findings raise suspicion for rectus sheath hematoma, ultrasonography and CT scanning are commonly used to help confirm the diagnosis. Before the advent of ultrasonography and CT scanning, the correct clinical diagnosis was only made in 17-40% of cases prior to exploratory laparotomy or death.

Ultrasonography

Ultrasonography can be used as a first-line diagnostic test for rectus sheath hematoma, or it can be used to monitor the evolution of a known hematoma. Ultrasonography provides rapid accurate information about the size, the location, and the physical characteristics of the mass. It is safe and well tolerated. It does not expose the patient to radiation or intravenous contrast material. The typical ultrasonographic findings are sufficient to establish the diagnosis.

See the image below.

Expected findings

Rectus sheath hematomas are described as spindle shaped on sagittal sections and as ovoid on coronal sections. Usually, the mass is sonolucent, although it may also be heterogenous, depending on the combined presence of clot and fresh blood.^[8]

Effectiveness

Ultrasonography has been reported to have a sensitivity of 85-96% in depicting rectus sheath hematoma. However, when it is unsuccessful, it often fails spectacularly, causing undue delay in treatment or unnecessary laparotomy. Zainea's case series of 4 patients in 1988 noted that findings from ultrasonography were misleading in 2 of them. In those 2 patients, the ultrasonographic report described the pathology as occurring within the peritoneal cavity, prompting unnecessary surgical intervention.^[9]

Role of ultrasonography

Ultrasonography should be used as a first-line diagnostic test in pediatric patients, pregnant patients, or perhaps in patients with renal insufficiency. However, in other patients, its primary role may be to follow hematomas to maturation and resolution after definitive diagnosis by CT scanning. In patients where the clinician has a moderate-to-high suspicion for rectus sheath hematoma, ultrasonography serves as a viable screening test. Therefore, even if the sonogram demonstrates a mass that is difficult to characterize as intraperitoneal or extraperitoneal, the clinician's pretest probability can help guide therapy. Caution should always be exercised with patients in whom infection or diagnostic uncertainty exists.

CT scanning

CT may be used as a first-line diagnostic procedure in the evaluation for rectus sheath hematoma, or it may follow nondiagnostic ultrasonographic findings. CT permits a precise determination of the location, the size, and the extension of the hematoma. Information is also obtained about the rectus abdominis muscle and the perimuscular tissue. CT may be more appropriate than ultrasonography as a first-line test because it simultaneously aids in the diagnosis of rectus sheath hematoma and rules out other abdominal pathology.

See the images below.

Expected findings

Characteristic findings of acute rectus sheath hematoma on CT include a hyperdense mass posterior to the rectus abdominis muscle with ipsilateral anterolateral muscular enlargement. Chronic rectus sheath hematoma may be isodense or hypodense relative to the surrounding muscle. Above the arcuate line, rectus sheath hematomas have a spindle shape, while those below the arcuate line are typically spherical.^[10]

Effectiveness

CT scanning is 100% sensitive and 100% specific in acute rectus sheath hematoma of less than 5 days' duration. After 5 days, MRI may be required to differentiate hematomas from tumors of the abdominal wall.

Types of rectus sheath hematoma on CT scanning

In 1996, Berna used the appearance of rectus sheath hematomas on CT scans to differentiate 3 levels of severity with disposition and therapeutic implications.^[2]

• 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.
• Type II: The hematoma is intramuscular (mimicking type I) but with blood between the muscle and the transversalis fascia. It may be unilateral or bilateral, and no blood is observed occupying the prevesical space. A fall in hematocrit may be observed.
• 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.

Role of CT

CT is the diagnostic test of choice for rectus sheath hematoma and is superior to ultrasonography in sensitivity and specificity. Patients who are pediatric, pregnant, or have renal insufficiency may benefit from ultrasonography as a first-line test to avoid radiation and intravenous contrast material. In patients with renal insufficiency, a noncontrast CT scan can be used and will still show the typical findings of rectus sheath hematoma, although the ability to find active extravasation or to rule out other abdominal pathology is limited.

MRI

MRI is useful in differentiating chronic rectus sheath hematoma from other anterior abdominal wall masses when CT findings are not specific. Chronic rectus sheath hematoma is demonstrated as high signal intensity on both T1- and T2-weighted images up to 10 months following the onset of the hematoma. In acute rectus sheath hematoma of less than 48 hours' duration, the MRI of rectus sheath hematoma does not reveal high signal intensity and is not useful in the diagnosis.^[11] Many clinicians will be limited by the availability of MRI in their practices, particularly when other types of imaging studies are readily available.

Plain anteroposterior (AP) and erect radiography of the abdomen

Plain AP radiographs are not useful in diagnosing rectus sheath hematoma, but they may help in ruling out other diagnostic possibilities if no free air, obstructive gas pattern, sentinel loop, appendicolith, or other findings are noted.

Lateral decubitus radiography

Lateral decubitus radiography is only of historical interest in diagnosing rectus sheath hematoma. In 1967, Herzan described a rectus sheath hematoma on a lateral decubitus radiograph as a placenta-shaped or ovoid spindle-shaped mass in the anterior abdominal wall or as a widening of the rectus sheath.^[12]

Scintigraphy

A solitary case report by Monsein and Davis in 1990 describes the use of this diagnostic modality in rectus sheath hematoma.^[13] Following positive evaluation by CT scanning of a large mass in the anterior abdominal wall, scintigraphy with technetium-99m–tagged red blood cells depicted several sites of bleeding corresponding to previous insulin injection sites. This bleeding was not observed with angiography. The inferior epigastric artery was embolized with Gelfoam despite an absence of bleeding on angiography with subsequent hematocrit stabilization. Therefore, scintigraphy can be used after a diagnosis of rectus sheath hematoma by CT to show active extravasation not detectable by angiography.

Cystography

Cystography should not be used to diagnose rectus sheath hematoma when the condition is suspected. However, a patient with primarily bladder symptoms may undergo diagnostic cystography. Rectus sheath hematoma can be observed as an indentation of the dome of the bladder, which can be mistaken for a pelvic tumor but is caused by dissection of the rectus sheath hematoma into the prevesicular space of Retzius.

Intravenous pyelography (IVP)

IVP should not be used to diagnose rectus sheath hematoma when the condition is suspected. However, patients with rectus sheath hematoma and significant dissection into the space of Retzius may present with an obstructive pattern of renal failure. Patients with obstructive renal failure who undergo IVP can show bilateral hydronephrosis if the rectus sheath hematoma significantly displaces the bladder.

• Intraluminal bladder pressure measurement: Measuring intra-abdominal pressure by using indwelling catheter manometry of the bladder may be considered if there is clinical suspicion of abdominal compartment syndrome. Clinical signs of abdominal compartment syndrome include oliguria, decreased cardiac output, alterations in minute ventilation, intracranial hypertension, and altered splanchnic blood flow. However, the incidence of abdominal compartment syndrome in rectus sheath hematoma is unknown.^[14]

• Needle aspiration: Needle aspiration of rectus sheath hematoma has occasionally been advocated to differentiate rectus sheath hematoma from an abscess and to decrease the duration of symptoms by the removal of the irritating mass. However, most sources consider needle aspiration unwise because of the risk of bacterial contamination and the possibility of bowel perforation if the mass is a hernia sac instead of a hematoma. Also, aspiration of clotted blood is difficult and likely to be unsuccessful. Some sources recommend needle aspiration under ultrasonographic guidance, although this technique still carries the risk of bacterial contamination. One case of hematoma recurrence has been reported following needle aspiration.