IMAGING IN PYOGENIC MENINGITIS

                          

Explore Imaging in pyogenic meningitis focusing on its meningeal anatomy, risk factors and etiology of infection, imaging and differential diagnosis. Learn the difference between types of meningeal enhancement and its causes.

Highlights

• 🧠 Imaging anatomy of the meninges.
• 🗺️ Epidemiology & clinical features of pyogenic meningitis
• 🔬 Difference between normal and abnormal leptomeningeal enhancement.
• 📸 Imaging cases of pyogenic meningitis using CT and MRI
• 💉 CSF findings in all types of meningitis
• ⚙️ Differential diagnosis
• 📅 Subscribe for more insights on radiology topics.

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Meningeal layers

Meninges contains of three layers

-          The outermost layer is the dura mater

-          Underneath the dura matter almost adherent to Dura we have arachnoid mater with a thin space in between

-          Next we have the piamater which adheres to the sulci and gyri

Pachymeninges is a collective term which indicates dura mater plus arachnoid mater

 Leptomeninges is a collective term to indicate arachnoid plus piamater

 

Extra-axial (Meningeal) spaces

1.      Epidural space: above the dura matter

2.      Subdural space: between the dura matter and arachnoid

3.      Subarachnoid space: beneath the arachnoid (contains the CSF )

 

Normal versus abnormal leptomeningeal enhancement

Meninges contains blood vessels and normally do enhance on the contrast enhanced CT and MRI. The normal meningeal enhancement appears as

-          Thin

-          Smooth

-          Short and discontinuous

-          Well demarcated

-          Symmetric enhancement

-          Short segment convexity of meningeal enhancement : less than 3 cm in a continuity

-          No Suprasellar or ventricular wall enhancement

In cases of abnormal meningeal enhancement there will be

-          Thick

-          Irregular

-          Nodular

-          Asymmetrical

-          Extend deep into the sulci

-          Long segment diffuse convexity meningeal enhancement : more than 3 cm length

-          Meningeal enhancement for three contiguous segments on 1.5 Tesla MR images in a sequence that shows abnormal leptomeningeal enhancement

Causes of meningeal enhancement

Pachymeningeal	Leptomeningeal
hypotension	infection
idiopathic	inflammatory cases
infectious diseases	acute stroke
inflammatory diseases like sarcoidosis	metastasis
metastasis
subarachnoid bleed

 Risk factors

-          Elderly patients

-          Immunocompromised patients

-          Diabetics

-          Suffering with malignancy

-          Alcoholism

 Etiology

depends on the age group in

-          Less than 2month old :Group B streptococcus

-          Older children and young adults: Neisseria meningitidis

-          Adults: Streptococus pneumoniae

-          Trauma or iatrogenically induced meningitis: Streptococcus

-          Immuno compromised patients: Listeria monocytogenes

Roots of spread of infection

-          Hematogenous dissemination: which is the most common type of spread

-          Direct implantation in cases of trauma rand iatrogenic cases

-          Local extension from the localized infections like sinusitis or orbital cellulitis, otitis media mastoiditis Etc

Clinical features

in any cause of leptomemingeal infection these are the common

In infants with leptomeningitis we can see altered state of consciousness, bulging fontanellae, failure to thrive, fever, irritability, seizures and vomiting

Kernig’s sign can be elicited on evaluation

In adults with leptomeningitis we can have fever, headache, meningismus or neck rigidity, photophobia

Kernig’s sign can be elicited

 Imaging modalities

Imaging is not usually used for initial diagnosis but it's used for confirming the suspected cases of meningitis and also to rule out meningitis mimics like neoplasm. Also we can evaluate the complications of meningitis and we can look for increased intracranial pressure before performing a lumbar puncture

The modalities which we use are CT especially contrast enhanced CT and contrast enhanced MRI. Newer sequences like magnetization transfer Imaging and diffusion tensor Imaging also are coming up.

1.      Non-contrast enhanced CT:

-          Sulcal effacement because of diffuse cerebral edema

-          Dilated ventricles or hydrocephalus which is a complication of meningitis

-          Sometimes we can see hyperdense meninges

2.      Contrast enhanced CT

-          Abnormal leptomeningeal enhancement along the cerebral convexity

-          Effaced sulcal spaces along basal cisterns which is mainly found in tubercular but also pyogenic menitis can show it

3.      Contrast enhanced MRI also has similar findings as CECT

CSF analysis correlation:

Complications of meningitis

1.     1. Hydrocephalus: Non-communicating or obstructive hydrocephalus
2.      Extra axial collections: Sterile (subdural effusion) or purulent (subdural empyema)
3.      Epidural or subdural abscesses
4.      Cerebritis and abscess formation
5.      Ventriculitis
6.      Thrombotic complication and infarcts
7.      Cranial nerve involvement usually found in viral meningitis 

Differential diagnosis

-          Tubercular meningitis

-          Fungal meningitis

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