Colloid Cyst of the Third Ventricle

Definition

Clinical Features

• Presentation:
  • generally third to fifth decades of life
  • manifestations of ventricular outflow obstruction:
    • due to intimate relation to foramen of Monro (Fig. 1
      

      Fig. 1: Colloid cyst. The obstructive ventricular dilatation (hydrocephalus) associated with this large example is characteristic of these lesions. Note the well-delineated cyst wall, bright in this contrast-enhanced magnetic resonance image.

      )
• Rarely:
  • adenocarcinomatous transformation1

Pathogenesis

• Ultrastructure2 and immunocytochemistry3,4 support origin from misplaced endodermal tissues

Gross Pathology

• Thin-walled
• Often draped by adherent choroid plexus
• Filled with viscous, mucoid material that rapidly congeals on fixation

Histopathology

• Lining epithelium:
  • columnar type:
    • when well preserved
    • frequently populated by ciliated and goblet cell elements (Fig. 2
      

      Fig. 2: Colloid cyst. A pseudostratified and ciliated columnar epithelium lines well-preserved colloid cysts. Note the supporting collagenous tissue of the cyst wall, yellow in this hematoxylin-phloxine-saffranin preparation.

      ):
      • basement membrane:
        • inapparent at light microscopic level
  • prone to low cuboidal attenuation:
    • due to pressure of cyst contents
• Delicate, fibrous capsule
• Cyst contents:
  • PAS positive
  • commonly hyphae-like aggregates of degenerate nucleoproteins:
    • so characteristic as to be diagnostic in absence of identifiable epithelium5 (Fig. 3
      

      Fig. 3: Colloid cyst. The radiate, hyphae-like structures shown here are often found admixed with the liquid contents of colloid cysts and, for practical purposes, are diagnostic of this entity.

      )
  • inflammatory reaction to contents when ruptured responsible for most, if not all, cases of xanthogranuloma in third ventricle6

Special Stains and Immunohistochemistry

• Constituent epithelial cell types:
  • correspond closely to those typical of respiratory mucosae:
    • apical glycocalyx coating particularly characteristic of endodermally derived epithelia
  • express:
    • cytokeratin
    • epithelial membrane antigen
    • carcinoembryonic antigen
  • do not express:
    • GFAP
    • choroid plexus-associated transthyretin (prealbumin)

Differential Diagnosis