Meningioma: A brief and simplified description

Meningiomas account for about 25% of primary intracranial tumours.  Meningiomas occur most commonly in middle-aged and elderly patients with a peak during the sixth and seventh decades. The term meningioma was coined by Harvey Cushing in 1922 when he reported 85 cases of meningioma. In 1932 Cushing & Eisenhardt reported a series of 313 patients with meningioma encountered between 1903 & 1932.
In 1932 Cushing wrote “ There is to day nothing in the whole realm of surgery more gratifying than the successful removal of a meningioma with subsequent functional recovery.” Most of meningiomas are cured if completely removed.

The anatomical distribution of intracranial meningiomas is as approximately as follows:

Convexity   ( Frontal , Parietal , Occipital , Temporal )             Commonest

Parasagittal ( Anterior 1/3^rd, Middle or posterior one third)                                                    

Falcine Meningioma (Anterior 1/3^rd, Middle or posterior one third)
(arises from the falx,  completely concealed by overlying cortex, & initially does not involve the superior sagittal sinus but later may involve the sinus).
Falcine meningiomas can be divided into anterior, middle and posterior types. Anterior third extends from the crista galli to the coronal suture, the middle third from coronal suture to the lambdoid suture and posterior third from the lambdoid suture to the torcula.

Shenoid ridge or sphenoid wing meningioma ( Pterional, Alar or Clinoidal) 

Olfactory groove meningioma                         

Tuberculum sellae ( 5% to 10% of intracranial meningiomas)
                                                                                                                            
Intraventricular  ( 1% of all  meningomas, 90% are located at the trigone of lateral ventricle)   

Cavernous sinus meningioma

Meningioma of the optic nerve and orbit                                                                                                                            

Infratentorial  : Cerebellopontine angle , petroclival, jugular foramen, foramen magnum and basal meningiomas.
                              

                                                                                                                    
Pathology

Meningioma arises from arachnoid cap cells. The arachnoid villi protrude into the venpous sinuses. The venous endothelium is in contact with some arachnoid villi cells ( arachnoid cap cells ).

Meningioma is usually a slow growing, extraaxial and  well circumscribed tumor. 

Usually benign ( 32% of incidentally discovered meningiomas do not grow over 3 years follow up ).

Typically tumor has broad based attachment on dura  and  enchances densely.

Intratumoral  calcification is very common.

Classic histological finding is the presence of psammoma bodies.

Meningiomas are multiple in 8% of cases.

Occasionally meningioma forms a diffuse sheet of tumor over the dura and is known as meningioma en plaque.

 Histologically ( WHO classification 2007) meningioma  can be classified

GRADE 1

Meningothelial ( Syncytial) meningioma

Fibrous ( Fibroblastic) meningioma

Transitional ( Mixed) meningioma

Psammomatous meningioma

Angiomatous meningioma

Microcystic meningioma

Secretory meningioma

Lymphoplasmacyte- rich meningioma

Metaplastic meningioma



Meningiomas  with greater likelihood of recurrence and/or aggressive behavior  are WHO grade II & grade III meningiomas

GRADE II

Atypical  meningioma

Clear cell  meningioma

Chordoid  meningioma

GRADE III

Rhabdoid meningioma

Papillary  meningioma

Anaplastic ( Malignant ) meningioma


In year 2016, World Health Organization has published an updated version of classification of tumors of central nervous system. The new classification is both a conceptual and practical advance over its 2007 predecessor. For the first time , the WHO classification uses molecular parameters in addition to histology. So, the new classification is a combined genotype and phenotype classification.  But the classification and grading of meningiomas did not undergo revisions except for the introduction of brain invasion as a criterion for the diagnosis of atypical meningioma, WHO grade II.

So, the 2016 WHO classification of Meningiomas is as follows:

Meningioma

Meningothelial meningioma

Fibrous meningioma

Transitional meningioma

Psammomatous meningioma

Angiomatous meningioma

Microcystic meningioma

Secretory meningioma

Lymphoplasmacyte-rich meningioma

Metaplastic meningioma

Chordoid meningioma

Clear cell meningioma

Atypical meningioma

Papillary meningioma

Rhabdoid meningioma

Anaplastic ( malignant) meningioma

Radiological Features of Meningioma :

Plain radiography usually shows hyperostosis, increased vascular markings and calcification
CT scan : Meningioma is an extraaxial lesion [( there is no parenchyma all round the tumor, as on one side it is based over the dura ( bone)]. A well marginated ,  isodense to slightly hyperdense lesion,  homogenously and intensely enhancing , with associated brain edema  . Tumor is extraaxial lesion  with broad base against a bony structure or dural margin. The involved dura also enhances on contrast administration ( Dural tail sign).The bone adjacent to the dural base may show bony erosion or hyperostosis.
MRI brain with contrast and digital substraction angiography (DSA) are the other investigations for the operative planning for intracranial meningiomas.

MRI brain should always be done before the surgery as it provides better anatomical details and also gives a clue about the vascularity and type of meningioma.  It is indispensible in cases of CP angle tumor, Clinodial meningioma, etc.

Treatment goal : Complete Surgical Excision.

Sometimes it is not possible to completely excise the lesion due to its location. Under these conditions a subtotal resection should be done to aim for the complete functional recovery. As meningioma is relatively a benign lesion and remaining tumor takes long time to recur, the safe limit of resection may be done.

Simpson classification of extent of resection for intracranial meningima

Grade 1                Gross total resection of tumor, dural attachment and involved abnormal bone
Grade II                Gross total resection of tumor & coagulation of dural attachment
Grade III               Gross total ( Macroscopic ) resection of tumor
Grade IV               Subtotal ( Partial ) resection
Grade V                Simple decompression

References:
H.Richard Winn’s Youmans Neurological surgery, Schmidek & Sweet operative Neurosurgical techniques.
Greenberg M.S., Handbook of neurosurgery, 7th ed. Thieme
WHO classification of tumors of the central nervous system,2007 ( 4th ed)
WHO classification of tumor of central nervous system, 2016 update
Review article :  David N.Louis et al. The 2016 World health organization classification of tumors of the central nervous system: a summary. Acta Neuropathol ( 2016) , 131: 803-820.