WHO Grade 1 Meningioma

see also WHO Grade 2 Meningioma and WHO Grade 3 Meningioma

WHO Grade 1 meningiomas are the most common and least aggressive subtype of meningiomas. They are classified as benign tumors based on histopathological and biological criteria defined by the World Health Organization (WHO).

A WHO Grade 1 meningioma is a slow-growing, well-differentiated tumor that originates from the meningothelial (arachnoid cap) cells of the dura mater. It typically shows no brain invasion and has a low risk of recurrence following complete surgical resection.

WHO Grade 1 includes the following subtypes:

• Meningothelial
• Fibrous (fibroblastic)
• Transitional (mixed)
• Psammomatous
• Angiomatous
• Microcystic
• Secretory
• Lymphoplasmacyte-rich
• Metaplastic

• Low mitotic index (<4 mitoses per 10 HPF)
• Absence of brain invasion
• Uniform nuclei, minimal pleomorphism
• Absence of necrosis and prominent nucleoli
• May contain psammoma bodies (calcifications)

• Growth: Typically slow-growing
• Location: Most often supratentorial (convexity, parasagittal, sphenoid ridge), but may occur anywhere along the meninges
• Symptoms: Related to mass effect—headache, seizures, focal neurological deficits
• Recurrence: Low after Simpson grade I or II resection

• Surgical resection is the treatment of choice
• Simpson grade I–III resection aims to minimize recurrence
• Adjuvant radiotherapy is not routinely indicated but may be considered in subtotal resection or recurrence

• Excellent prognosis with complete resection
• 5-year recurrence-free survival >90% for totally resected tumors
• Long-term follow-up recommended for subtotal resections

• WHO Classification of Tumours Editorial Board. *WHO Classification of Tumours of the Central Nervous System*. 5th ed. IARC, 2021.
• Goldbrunner R, et al. EANO guidelines for the diagnosis and treatment of meningiomas. *Lancet Oncol*. 2016.