Epidural Abscess

Etiology

Bacterial SEA is the primary cause of this entity. Tuberculous, fungal, and parasitic abscesses of the spinal epidural space typically evolve more insidiously than pyogenic bacterial ones. Other than Candida infections, these etiologies are more frequently encountered in tropical and subtropical, resource-constrained regions worldwide.[3][6]

IEA usually starts with an exogenous point of entry, either the paranasal sinuses or the ears. Streptococci, usually anaerobic forms, eg, Peptostreptococcus, and other anaerobes, eg, Cutibacterium (formerly Propionibacterium, part of the skin flora), are common organisms. Gram-negative bacilli or fungi can also be a cause. They usually originate in the sinuses.[7] Additionally, IEA can be a complication of neurosurgery, with the most likely organisms being staphylococci, especially Staphylococcus aureus, and gram-negative bacteria. Infection can also spread inward from osteomyelitis of the skull or fetal monitoring probes applied to the skull during birth.[4][8]

Epidemiology

The incidence of SEA ranges from 0.2 to 1.2 cases per 10,000 hospital admissions. Recognized risk factors include diabetes, intravenous drug use, chronic renal failure, alcoholism, and immunosuppression. SEA occurs 9 times more frequently than IEA and is more likely to present acutely.[9][10]

Although uncommon, IEA ranks as the third most common focal pyogenic intracranial infection, following brain abscess and subdural empyema. Historically, head and neck infections, eg, sinusitis, mastoiditis, and otitis, accounted for most cases; current patterns more often reflect complications arising from neurosurgical procedures.[11]

Pathophysiology

In epidural abscesses, the infection enters the epidural space by direct extension from a contiguous site or by hematogenous and lymphatic seeding from a remote site.[7] Contiguous infections include vertebral osteomyelitis, discitis, abscesses involving the retropharyngeal, perinephric, paraspinal, or psoas, decubitus ulcers, and persistent dermal sinus tracts. Local invasion from superficial infections can also occur following penetrating injuries, surgery, or spinal procedures. Such procedures might be as simple as a lumbar puncture or paravertebral injection, or as complex as epidural catheterization or computed tomography (CT)-guided needle biopsy.[9]

Approximately 25% to 50% of SEAs come from hematogenous spread into the epidural space. Of those, the majority (about 15%) are from skin or soft tissues. Endocarditis and infected intravascular catheters, respiratory tract infections, urinary tract infections, abdominal infections, dental abscesses, and complications from gastrointestinal surgery are also possible.[12]

IEA is mostly a localized lesion with a central collection of pus surrounded by a wall of inflammatory reaction. Dura is rigid and tight around the base of the skull, thereby preventing downward transmission of the infection into the spinal epidural space. SEA spreads quickly because the spinal epidural space is continuous, and the infection is more granulation tissue than purulent material.[13]

Histopathology

Blood and intraoperative cultures identify the etiologic organisms of an epidural abscess and its associated histopathology. Staphylococcus aureus (coagulase-positive or negative) accounts for over 60% of SEA cases. The polymicrobial SEA is a rarity, and blood cultures are positive in most patients. Furthermore, the pathogens identified by blood culture are almost always similar to those cultured from abscess content.[14] This situation differs completely from that of IEA, in which blood cultures are positive in only 10% of patients and, even when positive, do not represent the actual causative organism. In an IEA and a brain abscess, pus often grows mixed microorganisms.[13]

History and Physical

At initial presentation, patients with SEA often exhibit vague and subtle symptoms, requiring a high index of suspicion to establish the diagnosis before neurologic deficits develop. Localized vertebral tenderness on palpation or percussion almost always occurs and progressively worsens, becoming increasingly difficult to manage. Within a few days of the onset of spinal tenderness, 90% of patients develop radicular pain. Most patients also experience fevers exceeding 38 °C. Additional nonspecific symptoms may include generalized malaise, fatigue, headache, irritability, or vomiting.[5]

Heusner (1948) described the following clinical progression of SEA in 4 overlapping stages:

1. Spinal ache or back pain
2. Radicular pain
3. Weakness
4. Ultimately paralysis

The interval between the onset of back pain and the onset of neurologic deficits varies widely. Rapid progression from back pain to severe neurologic compromise or death underscores the need to include SEA in the differential diagnosis of any patient presenting with new or worsening back pain, particularly when accompanied by fever and localized spinal tenderness.[1][15]

Early back pain may remain indolent for weeks; however, severe pain commonly progresses to radicular symptoms within 3 to 4 days. Signs of spinal cord dysfunction typically follow within the next 4 to 5 days. Neurologic deficits at this stage may remain reversible. However, rapid surgical intervention often becomes necessary because progression to complete paralysis may occur within hours, regardless of the chronicity of the condition. Neurologic findings vary according to the level of spinal cord involvement and further influence the differential diagnosis at presentation.[16]

In IEA, symptoms arise from infection or from a gradual increase in ICP. Common symptoms include fever, headache, lethargy, nausea, vomiting, and photophobia. Frequent clinical signs include papilledema, sinus drainage, cranial nerve palsies, and focal neurologic deficits. IEA often develops as a complication of surgery or other invasive procedures, which complicates diagnosis due to the focus on the primary condition rather than the secondary infection. Any patient presenting with fever and headache warrants consideration of this diagnosis, especially following recent intracranial or head-and-neck surgery. Suspicion further increases in the presence of head and neck infection sources, eg, sphenoid or ethmoid sinusitis or chronic otitis media.[17]

Evaluation

Laboratory findings for these patients are typically nonspecific. Patients may have mild leukocytosis and elevated C-reactive protein. Blood cultures are positive in SEA but not so in IEA. Conventional radiography of the spine may not be helpful in SEA, as osseous destruction may be absent. Bone and gallium scans, as well as CT, are equivocal and can delay definitive diagnostic testing. The gold standard for diagnosing SEA is magnetic resonance imaging (MRI), which has almost completely replaced myelography. MRI is as sensitive and specific as CT-myelography.[18] For patients with IEA, CT or MRI can be used, with the latter providing more detailed information. Currently, CT-guided needle aspiration is increasingly used worldwide to evaluate both entities.[19]

Treatment / Management

Spinal Epidural Abscess

SEA can progress rapidly to catastrophic outcomes, with neurologic deterioration advancing to severe spinal cord dysfunction within a few hours. Such rapid progression necessitates immediate diagnosis and intervention. The management usually comprises decompressive surgery and drainage of the abscess (considered the gold standard in most circumstances), eradication of the primary underlying infectious focus (if detectable), and parenteral antibiotic therapy to target likely etiologic agents, eg, coagulase-negative staphylococci, streptococci, and gram-negative rods.

Most experts recommend treating posterior epidural abscesses by posterior laminectomy, drainage of infected and granulation tissue, and normal saline irrigation. The surgeon usually places a drainage system and continues to irrigate the abscess for several days postsurgery until the infection is completely resolved. A combination of third-generation cephalosporin (ceftriaxone) with another antimicrobial showing antistaphylococcal activity (rifampicin, nafcillin, or fosfomycin) is recommended. Clinicians should treat patients with antibiotic therapy for 4 to 6 weeks unless associated osteomyelitis is present, in which case treatment should be continued for 6 to 8 weeks.[1][20]

In select cases involving extensive posterior abscesses without significant spinal cord compression or neurologic deficits, CT-guided needle aspiration may serve as an alternative to surgery. Carefully selected patients without neurologic deficits, those with contraindications to surgery, or those who decline surgical intervention may receive high-dose antibiotic therapy alone; however, such approaches require cautious application due to the risk of clinical deterioration.[21](B3)

Intracranial Epidural Abscesses

IEA) typically involves a combination of surgical drainage and antibiotic therapy. Drainage may be achieved through craniotomy or burr hole procedures, with grafting or other occlusive techniques considered when the dura becomes involved. Antibiotic therapy should begin promptly after obtaining cultures and specimens. Since this is a relatively rare disease, information available for antibiotic choice is mostly anecdotal. Antibiotics should cover streptococcus, hemophilus, and anaerobes to treat infections that have spread from the ear, sinuses, or other areas of the head and neck.

Acceptable regimens include third-generation cephalosporins or vancomycin combined with metronidazole, followed by adjustment based on culture and sensitivity results.[22] Vancomycin demonstrates limited penetration across the blood-brain barrier, leading some clinicians to substitute rifampin, while others consider a short course of corticosteroids. Alternative agents, eg, linezolid and daptomycin, have been used, although supporting data remain limited. Intravenous antibiotic therapy typically continues for 6 to 8 weeks, as oral agents may not achieve adequate cerebrospinal fluid concentrations for definitive treatment. In pediatric patients with sinus-related IEA, effective sinus drainage without cranial procedures may suffice when no signs of increased intracranial pressure are present.[23][24](B3)

Differential Diagnosis

Clinicians should evaluate all patients presenting with acute or progressive back pain, fever, and localized spinal tenderness for SEA. Prompt consideration of the diagnosis remains essential despite the often subtle and variable clinical presentation. Classic signs and symptoms do not appear in every patient, which complicates early recognition. Children, in particular, may exhibit only atypical features. In patients with a chronic course, fever and systemic complaints may be minimal. Research series have noted that half of the patients with SEA are misdiagnosed during early evaluations.[25] IEA can mimic intracranial mass lesions, including primary or secondary brain tumors, abscesses, hematomas, or subdural empyema. The differential diagnosis also includes meningitis, vascular inflammations, and giant cell arteritis.[26]

Prognosis

With prompt and accurate diagnosis and time-sensitive management, the prognosis for both IEA and SEA is very good.[27]

Complications

Although uncommon, an epidural abscess represents a potentially devastating infection with life-altering neurologic complications. Early diagnosis and timely treatment can often prevent or reverse these outcomes, emphasizing the importance of rapid recognition. Following the diagnosis of SEA, clinicians should manage patients with the same urgency as for critically ill individuals. Despite appropriate recognition and intervention, some patients continue to experience severe neurologic complications. These complications may result from direct pressure causing spinal cord compression or from septic thrombophlebitis leading to ischemic necrosis. Spinal cord compression appears more common, whereas vascular compromise likely accounts for sudden deterioration in otherwise stable patients.[2][28]

Antibiotic therapy alone rarely suffices, as neurologic deficits may progress despite appropriate antimicrobial treatment. Complications can develop abruptly and unpredictably, and resulting paresis or paralysis may remain irreversible even with urgent surgical intervention.