The Diagnostic Approach to a Brain Abscess

Welcome to PICU Doc On Call, A Podcast Dedicated to Current and Aspiring Intensivists.

I'm Pradip Kamat coming to you from Children’s Healthcare of Atlanta/Emory University School of Medicine and I'm Rahul Damania from Cleveland Clinic Children’s Hospital. We are two Pediatric ICU physicians passionate about all things MED-ED in the PICU. PICU Doc on Call focuses on interesting PICU cases & management in the acute care pediatric setting so let’s get into our episode:

Welcome to our Episode about a 4-year-old girl with a chief complaint of headache and vomiting

Here's the case:

A 4-year-old presents to the PICU with headaches + vomiting and abnormal CT scan findings. The patient presented to the ED with h/o abdominal pain X 5 days with nonbilious, non-bloody emesis. Initial CBC, UA was normal. The patient was given some pain meds and IV fluids. Further history revealed that the patient has been having severe headaches for the last 5 days and had emesis secondary to the headaches resulting in generalized, non-specific abdominal pain. No h/o of trauma or seizures, no h/o of fever or diarrhea, no h/o toxic ingestions h/o recent travel, exposure to sick contacts, COVID test negative. No family h/o migraines, her immunizations are UTD. Besides the normal UA and CBC, her CMP was also normal.

A CT scan of the head revealed right frontoparietal mass with moderate surrounding edema, 6 mm leftward midline shift, diffuse sulcal narrowing, and right cisternal narrowing. Imaging of the abdomen (US and CT w/ contrast) was unremarkable. An MRI done revealed: Right parietal diffusion restricting lesion, most compatible with abscess. Moderate surrounding vasogenic edema. Given her abdominal pain- Abdominal KUB as well as contrast CT scan of abdomen and pelvis were performed and revealed no abdominopelvic pathology.

In the ED her vitals were normal and the patient was afebrile. On her PE: the patient appeared sleepy but woke up and answered questions appropriately. No focal deficits, PERRL, normal tone and strength. The rest of her physical exam was completely normal. She now is transferred to the PICU for serial neurological exams.

To summarize key elements from this case, this patient has:

• Headache with altered mental status
• No focal deficits
• Vomiting
• surprisingly no fever
• Imaging showing right frontoparietal mass.
• All of which brings up a concern for brain abscess
• This episode will be organized…
• Epidemiology and pathogenesis
• Diagnosis
• Management

Rahul, can you inform our listeners about the epidemiology of brain abscesses?

Only about 25% of brain abscesses occur in children. Incidence in developed countries is about 1-2% while in developing countries it's about 8%. Peak incidence in children is seen between the ages of 4-7 years and is more common in males. Brain abscess in the neonatal age group is rare but are associated with a higher risk of complications and mortality.

Risk factors for brain abscess include Otologic infections (ear, sinus, and dental infections), Congenital heart disease (30% of patients with BA have an underlying heart defect) with intra-cardiac or intrapulmonary shunting (pulmonary AV malformations in hemorrhagic telangiectasis), immunodeficiencies (solid organ transplantation, HIV, etc), prolonged steroid use, diabetes, alcoholism neurosurgical procedures, trauma. Other rare causes can be airway foreign bodies, congenital dermal sinuses, and esophageal procedures (such as dilatations).

Brain abscess typically begins with a localized area of cerebritis which evolves through various stages (typically 10-14 days) to develop into an encapsulated collection of purulent material with peripheral gliosis or fibrosis.

40-50% of the spread of infection is via a contiguous site of infection such as otitis, sinusitis or mastoiditis or from head trauma or neurosurgical procedure. 30-40% is spread through the hematogenous route from endocarditis, pulmonary infections, or dental abscess.

90% of brain abscesses in children are supratentorial. Mastoiditis, sphenoidal sinusitis, otitis media results in BA in the temporal lobe or cerebellum. Frontal lobe BA are due to frontal or ethmoid sinusitis or dental infections. BA from hematogenous spread results in multiple abscesses and typically follows the distribution of the middle cerebral artery including parietal and occipital lobes.

Rahul, what are some of the common pathogens seen in brain abscesses?

A meta-analysis reported the most common organisms in children with BA. These include streptococcus species seen in 36% (seen mostly with otologic infections, and strep viridans with endocarditis) followed by staphylococcal sp seen in 18% (head trauma, surgery, or skin infections) and gram-negative enteric bacteria seen in 16% (Proteus, Klebsiella, E. coli and Enterobacteriae. Citrobacter, E Coli, or proteus species are seen in neonates.

BAs from opportunistic microorganisms are usually multiple. They can occur in HIV-positive children with a low CD4 count; the most common pathogens are Toxoplasma, Nocardia, and Mycobacterium spp. Fungal abscesses (mainly Aspergillus or Candida) typically affect solid organ transplants recipients or children treated for leukemia

To summarize, altered mental status in a patient who is immunocompromised, think of opportunistic infections. Remember these patients can present even without a fever!

Rahul, what are some of the typical clinical features seen in patients with a brain abscess?

Clinical features would depend on site, size, involvement of surrounding area, patient’s immune status, and organisms involved. Fever with headache is typical. Vomiting is usually associated with headaches. Neurological manifestations include-Seizures, hemiplegia, cranial nerve palsies, and altered level of consciousness ranging from drowsiness to coma. Neonates can have bulging fontanelle and even increased head circumference.

The classic triad of fever +headache +neurological deficits is clinically seen in a small percentage (~33%) of patients. Frontal abscesses may remain asymptomatic especially if they are small. Pott's Puffy tumor also called Pott's edematous tumor (PET), is a sub-periosteal abscess of the frontal bone, associated with osteomyelitis of the frontal bone. which can give rise to BA. Meningeal signs are seen in 25% of patients with BA.

To summarize, Pott puffy tumor is osteomyelitis of the frontal bone with associated subperiosteal abscess causing swelling and edema over the forehead and scalp. It is a complication of frontal sinusitis or trauma.

If you had to work up this patient with a brain abscess what would be your diagnostic approach?

• I would start with a CBC with diff, Blood Cx, ESR, CRP, and CMP. Such tests are abnormal in only 20% of pediatric patients with BA.
• After CT or MRI, an LP can be attempted. LP would be contraindicated if there is a non-communicating obstructive hydrocephalous and brain shift. CSF fluid analysis, gm stain, and cultures could be helpful to find an organism and tailor therapy. Although CSF studies can be normal in 30% of patients with a BA. The sudden worsening of a preexisting headache can indicate a rupture of the brain abscess into the ventricular space or impending herniation from the lesion’s mass effect. Significant alteration in mental status is an ominous clinical finding. Abscesses located within their brainstem typically present with fever, headaches, hemiparesis, and focal cranial nerve findings involving CN III, CN VI, and CN VII.

• MRI is considered as the gold standard (low radiation risk, better resolution, and lower toxicity of contrast compared to CT). MR imaging may require sedation and take a longer time compared to CT (which is readily available and may not require sedation due to the speed of image acquisition and can be performed quickly prior to an LP). MR has higher sensitivity and specificity in the differential diagnosis with cystic or neoplastic lesions. An MR study for bacterial BA will show a necrotic center with the low signal at the DW-MR (diffusion-weighted magnetic resonance) and a T2-hypointensity with enhancement for the peripheral capsule. Fungal abscesses show a hypointense center in the T2-weighed image with variable expression in DW-MR.
• CT may reveal a mass lesion but MRI will help confirm the diagnosis and characterize the abscess better. Pus obtained from the aspiration or biopsy during the operating room can be used for culture.
• Cultures (for aerobic and anaerobic bacteria, Mycobacterium, fungi, protozoa), Gram, and special stains (for fungi, Mycobacterium, Nocardia) and polymerase chain reaction should be performed on blood, CSF, and pus of the cerebral abscess. It is best to involve our ID colleagues in a patient with BA to guide diagnostic studies as well as therapies. The culture positivity of blood and CSF samples is low (22-28% of cases). The rate of micro-organism isolation from abscess samples is about 60–80%, with polymicrobial involvement in about 20–30% of cases.
• Other studies can be obtained on a case-by-case basis depending on the primary focus would include an echocardiogram, CXR, abdominal US or CT, and bone imaging.
• Besides infectious disease and NS experts, consults with cardiology, hematology, OMFS, and ENT experts may be required.

To summarize, your approach to brain abscesses involves imaging, isolation of the lesion, and fluid/tissue diagnosis. Diagnostics such as an echo may reveal a primary source. This is definitely a coordinated effort with ID, neurosurgery, as well as neurology. These patients may also require prophylactic anti-epileptics peri-biopsy.

If our history, physical, and diagnostic investigation led us to brain abscess as our diagnosis what would be your general management of framework?

As we have mentioned before, A multidisciplinary team approach involving the PCCM, NS, ID, radiologists, and pharmacists are required for the successful management of patients with BA in the PICU.

Again, good basic PICU care with close attention to airway patency, adequacy of oxygenation/ventilation as well as stability of hemodynamics should be the first line approach in such patients admitted to the PICU. Good access for medication administration may include the need for a PICC line. Attention to neuro-status by frequent physical exams including attention to the patient's handling of oral secretions should be a priority. Continuous EEG may be required depending on the site, size, and involvement of the surrounding area.

Long-term antibiotics are the mainstay of therapy: A combination of vancomycin+ceftriaxone and metronidazole for 4-6 weeks if surgically drained vs 8 weeks for those without surgical drainage. Along the same lines, it is important to anticipate PICC lines or stable central lines for the long-term abx therapy.

Non-operative approach can be considered in patient with multiple small abscess or a single abscess which is < 2.5cm. Non surgical approach is also considered in patients with surgically inaccessible lesions, early cerebritis, or medical comorbidities that puts patient at high surgical risk.

What about operative approach?

Operative approach involves aspiration (typically CT guided), or excision. Aspiration results in removal of infected nidus (source control) as well as provision of material for gm stain/Cx. Excision of the abscess cavity may be useful when it is located in a periventricular or posterior fossa distribution, is loculated, or contains a foreign body. Excision should also be considered for abscesses that enlarge after 2 weeks of antibiotic therapy or that fail to shrink after 3 to 4 weeks of antibiotics. Primary excision may be the procedure of choice for lesions located in the cerebellum. Compared to aspiration, excision of BA in nonvital areas of brain had a lower rate of re-operation, a higher rate of postoperative abscess clearance, and better neurologic improvement after 1 month with no difference in long-term neurological outcomes or mortality.

Rahul, what are some of the prognostic features of BA?

BA from a contiguous focus of infection and those developing after a traumatic injury tend to have a better prognosis. Poorer prognosis is associated with delayed diagnosis, immunocompromised status, rupture of the abscess into the ventricular space, fungal etiology, and pretreatment neurologic compromise.

Let’s summarize

1. The classic triad of diagnosis of BA- headache +fever+ neurological deficit is seen in only 1/3rd of the patients with BA. Therefore a high index of suspicion is required based on patients risk factors such as immunosuppression, cyanotic heart disease etc.
2. Early imaging with CT/MRI is necessary to diagnosis
3. Antibiotic therapy should not be delayed. Triple therapy with vancomycin +ceftriaxone and metronidazole is typically initiated at diagnosis.

This concludes our episode on brain abscesses. We hope you found value in our short, case-based podcast. We welcome you to share your feedback, subscribe & place a review on our podcast! Please visit our website picudoconcall.org which showcases our episodes as well as our Doc on Call management cards. PICU Doc on Call is co-hosted by myself Dr. Pradip Kamat and Dr. Rahul Damania. Stay tuned for our next episode! Thank you!

References

• Fuhrman & Zimmerman - Textbook of Pediatric Critical Care Chapter 67 Central nervous system infections and related conditions (Havlin KM et al.)
• Reference 1: Mameli, C., Genoni, T., Madia, C. et al. Brain abscess in pediatric age: a review. Childs Nerv Syst 35, 1117–1128 (2019).
• Reference 2: Panda PK, Natarajan V, Vigneshwar NKV, Sharawat IK. Clinical Presentation and Outcome of Children with Brain Abscess. Ann Indian Acad Neurol. 2021 Nov-Dec;24(6):951-952. doi: 10.4103/aian.AIAN_794_20. Epub 2021 Jan 19. PMID: 35359509; PMCID: PMC8965945.