Perirectal Abscess Workup
- Author: Walter W Valesky Jr, MD; Chief Editor: Steven C Dronen, MD, FAAEM more...
Laboratory Studies
Many patients with perianal abscesses present as outpatients and need no laboratory blood tests as incision and drainage is sufficient. For these patients presenting to the emergency department with no signs of systemic disease, this management strategy may be adequate as laboratory data reveal very little additional information.
Complete blood cell count with differential may be obtained and may show leukocytosis or left shift with perirectal abscess or systemic disease, but the absence of these findings does not preclude either of these entities. As many as 23% of patients with diagnosed perirectal abscesses have shown normal temperature and a normal white blood cell count with a normal differential.[2]
Even though presumptive antibiotics are not required with routine incision and drainage of uncomplicated perianal abscesses,[16, 17] wound cultures should be collected in all patients in whom incision and drainage is performed as new strains of bacteria such as MRSA are being recognized as the etiology of perirectal abscesses[6, 7] and recurrence rates are as high as 10%.[1] Blood cultures may obtained but may be of little to no yield, with one study describing no growth on blood cultures.[2]
Imaging Studies
When not obviously apparent and with high clinical suspicion, imaging may be necessary for the diagnosis of perirectal abscesses. Plain films are of little usefulness in the diagnosis and should not be obtained unless other diagnoses are being considered.
CT scanning is readily available in most emergency departments (EDs) and is commonly used in the diagnosis of perirectal abscess. In one retrospective study, CT scanning for perirectal abscesses confirmed by surgical drainage yielded a sensitivity of 77%, with the false-negative patients being significantly more likely to be immunocompromised.[18]
While not readily used for this purpose in the ED, transperineal ultrasonography has shown good results for the detection of fistulous tracts and fluid collections in preoperative planning, with high sensitivities of 85%[19, 20, 21] and in one study was 100% sensitivity for the detection of surgical significant disease.[22]
MRI is the criterion standard for imaging of perirectal abscesses, with uses in preoperative planning at a sensitivity of 91%[23] ; however, its use is restricted in the ED.
Procedures
Common to the treatment of all abscesses is an adequate incision and drainage (I&D). The majority of perirectal abscesses require I&D in an inpatient setting, which may include seton placement, fistulectomy, fistulotomy, fibrin plug, or fibrin glue, depending on the location of the abscess or whether or not a fistula has formed.[2, 4] If the abscess is in a perianal location, I&D in the emergency department may be considered. To shorten the length of any potential fistula formation, the incision should be performed as close to the anus as safely possible.[1]
Adequate analgesia before aspiration is mandatory.
Lidocaine (2%) with epinephrine subcutaneously over and around the periphery of the abscess and intramuscular or intravenous narcotics are recommended.
Ethylene chloride spray applied to the suspected area immediately before aspiration may also be helpful in decreasing the discomfort of aspiration. The cooling effect of ethylene chloride renders pain receptors temporarily unable to transmit pain signals to the cerebral cortex.
Conscious sedation may also be used if the physician is trained and prepared to manage the airway. If this route is taken, cardiac monitoring, pulse oximetry, and airway management equipment must be available, including suctioning devices, bag-valve-mask, and endotracheal intubation equipment. This technique should only be used by physicians highly skilled in cardiac and airway management.
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