Diagnostic Approach to Intraparenchymal Brain Masses

Primary CNS Neoplasms

The American College of Radiology suggests that glioblastoma is the most common primary malignant brain neoplasm and should be at the top of the differential for an enhancing intraparenchymal mass 2, 3
Glioblastoma typically presents with irregular ring enhancement, surrounding vasogenic edema, and mass effect, with location at the subcortical gray-white junction being characteristic 1
Advanced imaging with perfusion MRI shows elevated relative cerebral blood volume (rCBV), helping differentiate glioblastoma from other entities 2, 4
Primary CNS lymphoma should be strongly considered, particularly in older patients or immunocompromised individuals, and characteristically shows homogeneous enhancement, often periventricular in location 1
Perfusion imaging can help differentiate primary CNS lymphoma from glioblastoma, with lymphoma typically showing lower rCBV 2

The central cavity of an abscess characteristically demonstrates restricted diffusion with low apparent diffusion coefficient (ADC), unlike most brain metastases or necrotic tumors 1
Abscess presents with rim enhancement and surrounding vasogenic edema, mimicking necrotic tumors, and history and clinical presentation help distinguish from neoplasm 1
Fungal infections, toxoplasmosis, and tuberculomas should be considered, especially in immunocompromised patients, and may present as single or multiple ring-enhancing lesions 1

Tumefactive multiple sclerosis can mimic intraparenchymal tumors, typically showing incomplete rim enhancement with the open ring facing the cortex, and additional smaller periventricular lesions perpendicular to the corpus callosum ("Dawson's fingers") 5
CSF analysis showing oligoclonal bands and elevated IgG index supports MS diagnosis 5
Neurosarcoidosis can present as single or multiple enhancing parenchymal masses, often involves leptomeninges and cranial nerves, and systemic workup for sarcoidosis is warranted 1

Subacute ischemic infarcts can mimic brain metastases as infarcted tissue begins to enhance following the acute phase, and are distinguished by wedge-like shape involving white matter and overlying cortex 1
Surveillance imaging shows regression of enhancement over time, unlike tumor 1

The American College of Radiology recommends obtaining MRI brain without and with IV contrast using standardized Brain Tumor Imaging Protocol (BTIP), including essential sequences such as high-resolution 3D T1 pre- and post-contrast, axial 2D T2 FLAIR, diffusion-weighted imaging (DWI) with ADC maps, susceptibility-weighted imaging (SWI), and axial T2 4, 3
Perfusion MRI (DSC or ASL) helps differentiate high-grade glioma from lymphoma and abscess, and MR spectroscopy can identify characteristic metabolite patterns 2, 4
CSF analysis with cytology, cell count, protein, glucose, and oligoclonal bands is recommended when diagnosis remains uncertain, with a minimum of 5-10 mL of CSF collected for optimal diagnostic yield 7, 5