Epidural brain abscess

Symptoms and Course of Epidural Brain Abscess

The clinical presentation of an epidural brain abscess is often insidious and nonspecific, frequently masked by the symptoms of the underlying primary infection (e.g., otitis media, sinusitis, mastoiditis). Many cases are asymptomatic or present with subtle signs [4]. When symptoms do occur, they can include:

• Headache: Often the most common symptom. Typically localized to the affected side, may be persistent, dull or throbbing, and potentially worse at night or with straining.
• Fever: May be present but is often low-grade or absent (< 50% of cases), especially if the primary infection is chronic or partially treated [5].
• Localized Tenderness: Pain or tenderness on palpation over the affected area (e.g., mastoid process in otogenic cases). Pott's puffy tumor (forehead swelling due to subperiosteal abscess) can be associated with frontal sinusitis complicated by epidural abscess.
• Ear Discharge (Otogenic): A sudden increase or change in character (e.g., profuse, pulsatile pus) of ear discharge in the context of otitis media can be suggestive, particularly if it follows a period of decreased discharge coinciding with worsening headache (a sign known as Gradenigo's triad when associated with abducens palsy and facial pain).
• General Malaise: Patients may feel generally unwell or lethargic.

Pain radiating to specific areas, such as the forehead, orbit, or teeth (Gradenigo's syndrome, involving petrous apex inflammation affecting the trigeminal and abducens nerves), can indicate a deeply located abscess near the petrous apex.

Signs of increased intracranial pressure (ICP) or focal neurological deficits are typically absent in uncomplicated epidural abscesses because the collection is outside the dura and usually does not cause significant brain compression unless very large or associated with other complications (e.g., venous sinus thrombosis) [2]. However, rarely, symptoms like significant lethargy, nausea, vomiting, bradycardia, or even papilledema (optic disc swelling) might occur, usually suggesting progression to a more severe complication like a subdural empyema, brain abscess, or significant venous sinus thrombosis.

 

Diagnosis of Epidural Brain Abscess

Diagnosing an epidural brain abscess preoperatively can be challenging due to the frequent lack of specific symptoms. Many are discovered incidentally during surgery for the primary infection (e.g., mastoidectomy). However, a high index of suspicion is warranted in patients with risk factors (otitis, sinusitis, trauma) who present with persistent localized headache, fever, and signs related to the primary infection (e.g., profuse ear discharge, mastoid tenderness).

Differential Diagnosis of Epidural Collections/Enhancement

 

Neuroimaging, particularly Magnetic resonance imaging (MRI) with contrast, is the cornerstone for diagnosing a suspected epidural abscess and differentiating it from other conditions.

The definitive diagnosis relies on neuroimaging:

• MRI with Gadolinium Contrast: This is the most sensitive imaging modality [6]. It typically shows a lenticular (lens-shaped) or layered collection located between the inner table of the skull and the dura mater, which is often displaced inward. The collection itself may appear isointense to slightly hyperintense relative to CSF on T1-weighted images and hyperintense on T2-weighted images. Crucially, following contrast administration, there is typically **enhancement of the inflamed dura mater** adjacent to the collection (representing the abscess 'wall'), and sometimes enhancement of the overlying pericranium or inflamed soft tissues. Diffusion-weighted imaging (DWI) can be helpful; pus within the collection typically restricts diffusion (appearing bright on DWI, dark on ADC maps), helping differentiate it from sterile fluid collections or chronic hematomas [7].
• CT Scan with Contrast: While less sensitive than MRI, particularly for smaller collections or subtle dural enhancement, CT can often detect epidural abscesses. It may show a low-density (hypodense) lenticular collection adjacent to the skull. Contrast enhancement of the displaced, thickened adjacent dura is the key finding, though may be subtle. CT is also excellent for evaluating associated bony erosion from the primary infection (sinusitis, mastoiditis) or skull fractures.
• MR Angiography (MRA) / CT Angiography (CTA) / MR Venography (MRV): These vascular imaging studies may be performed if associated dural venous sinus thrombosis (e.g., sigmoid sinus thrombosis in otogenic cases) is suspected, as this is a common and serious complication.
• Laboratory Tests: Blood tests (CBC, ESR, CRP) may show signs of inflammation but are nonspecific. Blood cultures are indicated if sepsis is suspected but are often negative in localized epidural abscess. Lumbar puncture is generally not helpful for diagnosing epidural abscess itself and potentially dangerous if there is significant unsuspected mass effect or progression to subdural/intracranial infection; CSF findings are typically normal or show only mild reactive changes unless meningitis co-exists.
• Intraoperative Findings: Confirmation often occurs during surgery for the primary infection (e.g., mastoidectomy) when pus is encountered between the bone and the dura after removal of infected bone or granulations.

Delaying diagnosis and treatment can lead to progression and the development of more severe complications, including meningitis, subdural empyema, intraparenchymal brain abscess, dural venous sinus thrombosis, sepsis, or cranial nerve palsies.

 

Treatment of Epidural Brain Abscess

The cornerstone of treatment for epidural brain abscess is **surgical drainage combined with appropriate antibiotic therapy** and **treatment of the underlying source infection** [8].

• Surgical Drainage: The primary goal is to completely evacuate the purulent collection and, critically, to address and eradicate the underlying source of infection.
  • For otogenic or sinusitis-related abscesses, surgery typically involves treating the primary site (e.g., complete mastoidectomy for mastoiditis, endoscopic or open sinus surgery for sinusitis). During this procedure, the surgeon removes the infected bone adjacent to the dura mater until the extent of the epidural collection is defined and healthy, non-inflamed dura is exposed peripherally. The pus is evacuated, granulation tissue debrided, and the area may be irrigated. Samples of pus and tissue should be sent for culture (aerobic, anaerobic, fungal if indicated).
  • If the abscess is related to trauma or neurosurgery, or if it is very large or inaccessible via the primary infection route, a separate neurosurgical approach (craniotomy or craniectomy) may be necessary specifically to drain the epidural space and debride infected tissue.
  • The dura mater itself is usually left intact unless there is obvious evidence of dural penetration, necrosis, or suspected subdural infection.
• Antibiotic Therapy: Broad-spectrum intravenous antibiotics should be started empirically as soon as the diagnosis is suspected (ideally after obtaining cultures if possible without significant delay). The regimen should cover likely pathogens based on the presumed source (e.g., coverage for common ear/sinus pathogens like Streptococci, Staphylococci, Haemophilus influenzae, anaerobes). Vancomycin is often included initially to cover MRSA, especially if trauma/surgery related or in high-prevalence areas. Therapy should be tailored once culture results and sensitivities from surgically obtained pus are available. A prolonged course of IV antibiotics (typically 4-6 weeks, sometimes longer) is generally required, with duration guided by clinical response, inflammatory markers, and imaging follow-up showing resolution [9].
• Supportive Care: Management of pain, fever, and hydration is important. Anticonvulsants are typically not required unless seizures occur or there is progression to subdural/intracranial involvement.

During surgery for the primary infection (e.g., mastoidectomy), if an epidural abscess is encountered, the surgeon must ensure wide exposure of the involved dura mater until healthy tissue margins are reached circumferentially. Puncture of adjacent dural venous sinuses (like the sigmoid sinus) is generally avoided unless thrombosis is strongly suspected based on preoperative imaging or intraoperative findings (lack of bleeding upon needle aspiration, palpable clot), as puncture carries risks of hemorrhage or further septic embolization. If meningeal signs are present suggesting possible concomitant meningitis, appropriate antibiotic coverage penetrating the blood-brain barrier is essential, and CSF analysis via LP may be considered *if imaging rules out significant mass effect*.

With prompt surgical drainage addressing the source and appropriate antibiotic therapy, the prognosis for uncomplicated cranial epidural brain abscess is generally very good, with low mortality and often complete recovery [10]. Delay in treatment or the presence of associated complications (subdural empyema, brain abscess, sinus thrombosis) significantly worsens the prognosis, increasing morbidity and mortality.

Attention! While often less dramatic initially than other intracranial infections, an epidural abscess requires urgent medical attention. Symptoms like persistent localized headache, fever, or changes in ear/sinus discharge, especially in the context of recent infection or trauma, should prompt immediate medical evaluation. Early diagnosis and treatment are key to preventing serious complications. Always consult qualified medical professionals for diagnosis and management.

References

1. Chapter on Intracranial Infections. In: Aminoff MJ, Josephson SA. Aminoff's Neurology and General Medicine. 6th ed. Academic Press; 2021.
2. Osborn AG, Salzman KL, Jhaveri MD, et al. Osborn's Brain. 2nd ed. Elsevier; 2018.
3. Brouwer MC, van de Beek D. Epidemiology, diagnosis, and treatment of brain abscesses. Curr Opin Infect Dis. 2017;30(1):129-134. doi: 10.1097/QCO.0000000000000334
4. Greenberg MS. Handbook of Neurosurgery. 9th ed. Thieme; 2020.
5. Nathoo N, Nadvi SS, van Dellen JR, et al. Craniospinal epidural abscess: a review of 53 cases and description of a novel classification system. J Neurosurg Spine. 2011;15(1):105-13. doi: 10.3171/2011.3.SPINE10530
6. Yousem DM, Grossman RI. Neuroradiology: The Requisites. 4th ed. Elsevier; 2016.
7. Lai PH, Hsu SS, Ding SW, et al. Brain abscess and necrotic brain tumor: discrimination with proton MR spectroscopy and diffusion-weighted imaging. AJNR Am J Neuroradiol. 2002;23(8):1369-77.
8. Chapter 91: Brain Abscess and Other Parameningeal Infections. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Elsevier; 2020.
9. Sexton DJ, et al. Spinal epidural abscess. UpToDate. Accessed [Insert Access Date - e.g., April 20, 2024]. (Subscription required - principles often similar to cranial)
10. Germiller JA, Monin DL, Sparano AM, et al. Intracranial complications of sinusitis in children and adolescents and their outcomes. Arch Otolaryngol Head Neck Surg. 2006;132(9):969-76. doi: 10.1001/archotol.132.9.969
11. Tunkel AR, et al. Practice guidelines for the management of bacterial meningitis. Clin Infect Dis. 2004;39(9):1267-84. doi: 10.1086/425368
12. Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor's Principles of Neurology. 11th ed. McGraw Hill; 2019.
13. Lai PH, et al. Brain abscess and necrotic brain tumor: discrimination with proton MR spectroscopy and diffusion-weighted imaging. AJNR Am J Neuroradiol. 2002;23(8):1369-77.
14. Lai HC, Tseng YC, Chen CJ, et al. Imaging of Brain Abscesses. J Radiol Sci. 2011;36:120-125.