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).
Definition
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.
Histological Subtypes
WHO Grade 1 includes the following subtypes:
- Meningothelial
- Fibrous (fibroblastic)
- Transitional (mixed)
- Psammomatous
- Angiomatous
- Microcystic
- Secretory
- Lymphoplasmacyte-rich
- Metaplastic
Histopathological Features
- 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)
Clinical Behavior
- 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
Treatment
- 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
Prognosis
- Excellent prognosis with complete resection
- 5-year recurrence-free survival >90% for totally resected tumors
- Long-term follow-up recommended for subtotal resections
References
- 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.