The postoperative MRI (Fig. 10.2) reveals complete resection of the tumor. The histopathological study is diagnostic for a World Health Organization grade I transitional meningioma.

• Meningioma: In the pineal region, meningiomas usually arise from tentorium cerebelli and falx. Few cases described without dural attachment are located in the velum interpositum.1,2
  
• Pineoblastoma: Most are large, greater than 3 cm with peripheral calcifications. Usually associated with obstructive hydrocephalus.
  
• Pineocytoma: An enhancing, well-circumscribed pineal tumor with calcifications that rarely extends into the third ventricle.
  
• Germ cell tumors: Engulf the pineal gland. Hyperintense to gray matter
  
• Astrocytoma: Arises from midbrain tectum or thalamus; rarely from the pineal gland
  
• Ependymoma: Mild to moderate heterogenous enhancement
  
• Metastases

• Because neuroimaging alone is not consistently diagnostic for third ventricular meningioma, these lesions are usually evaluated according to standard algorithms for pineal masses.
  
• Alfa-fetoprotein and beta human chorionic gonadotropin are markers of germ cell malignancy and should be measured in serum and cerebrospinal fluid if possible because patients with elevated markers suggestive of germinomas can be treated with chemotherapy and radiation without histologic diagnosis.
  
• For patients with a previous history of malignancy, a complete metastatic workup should be done.
  
• Also consider a spinal survey MRI.

• Stereotactic–guided biopsy
  
  
  
  • Ideally suited for patients with contraindications to open surgery and general anesthesia. Also for tumors that clearly invade the brainstem.³
    
  • However, it provides limited amount of tissue from lesions that may be histologically diverse.
    
  • The potential of hemorrhage is increased in the pineal region compared with other locations.⁴
  
  
• Open surgical resection
  
  
  
  • The selection of surgical approaches is determined according to
    
    
    
    • The relationship of the tumor to the deep venous system and other surrounding structures
      
    • Particular characteristics of the tumor (size, spread, etc.)
      
    • Degree of surgeon’s familiarity
  
  
• Approaches include (Fig. 10.3)
  
  
  
  • Infratentorial supracerebellar approach
    
    
    
    • For tumors that displace the internal cerebral veins dorsally
      
    • Tumor is reached through the midline, below the deep cerebral veins
      
    • Avoids violation of normal tissues
    
    
  • Occipital transtentorial
    
    
    
    • For lesion above the deep venous system, midline, or above the tentorial edge
      
    • With this approach, it is difficult to dissect the tumor from the tela choroidea of the third ventricle
      
    • Necessitates retraction of the visual cortex
    
    
  • Posterior transcallosal
    
    
    
    • For lesions anterior to the confluence of the deep cerebral veins
      
    • For lesions that displace the internal cerebral veins ventrally
  
  
• Because of its relatively small size, the tumor was approached through an infratentorial supracerebellar corridor, avoiding violation of normal tissues.

• The pineal gland is attached to the posterior wall of the third ventricle and projects posteriorly in the quadrigeminal cistern.
  
• The splenium of the corpus callosum lies above this region and the thalamus is located on each side.
  
• The roof of the third ventricle is formed by the body and crura of the fornices, the dorsal and ventral layers of the tela choroidea. The space between these two layers is the velum interpositum. The internal cerebral veins and the medial posterior choroidal arteries course through this space.
  
• The vein of Galen is located behind the posterior wall of the third ventricle.⁵

• Oculomotor deficits including Parinaud syndrome
  
• Injury of the deep venous system
  
  
  
  • Venous sinus tear
    
  • Venous infarction
    
  • Venous air embolism
  
  
• Infratentorial–supracerebellar approach: related to the sitting position
  
• Transcallosal approach: hemisensory or motor deficit (brain retraction), venous cortical infarction, disconnection syndrome
  
• Transtentorial approach: Visual-fields deficit, venous cortical infarction

• This case represents a meningioma of the third ventricle without dural attachment.
  
• Meningothelial cells are normally found in the arachnoid and choroidal tela. During embryologic development, arachnoid tissue migrates together with the choroid plexus as the ventricular system invaginates, and thus meningocytes are found in the stroma of the choroid plexus.6
  
• Ventricular meningiomas arise from choroid plexus or from the tela choroidea.⁶
  
• The velum interpositum is the potential space between the dorsal and ventral layers of the tela choroidea. In the present case, it is presumed that the meningioma originated from arachnoid cap cells of the dorsal tela choroidea of the third ventricle with ventral displacement of the internal cerebral veins.²

• Meningiomas rarely occur in cerebral ventricles.
  
• They are more commonly seen in the atrium of the lateral ventricle and for unknown reasons more frequently on the left side.⁶ They have also been found in the third ventricle, and only few cases have been reported in the fourth ventricle.⁶