====== 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.