Myxopapillary Ependymoma

Definition

Clinical Features

• Location:
  • virtually restricted to conus medullaris and filum terminale1,2
  • exceptionally cervicothoracic spinal cord
  • intracranial presentation exceedingly rare3
• Typically unusual extradural ependymomas that arise in subcutaneous tissues overlying:
  • sacrococcyx4,5
  • less often, in sacrum proper6
• Mainly adults in third to fifth decades of life
• Nearly 20%1 <20 years of age (some children)
• Nearly all produce:
  • low back pain
  • other manifestations including:
    • sciatica
    • sensorimotor deficits
    • impotence
    • urinary and fecal incontinence
• Occasionally spread to higher levels of central neuraxis via CSF
• Rarely metastasize to:
  • lungs
  • liver
  • lymph nodes
  • bone2,7
    • typically complicates stubbornly recurring tumors that have gained access to extravertebral soft tissues
    • more common if extradural variant arising in sacrococcygeal region5,6
    • neuroradiologic survey of spinal axis mandatory on diagnosis8

Pathogenesis

• Probably originate from:
  • ependymal rests representing remnants of extradural filum terminale, or
  • coccygeal medullary vestige
    • a derivative of the caudal neural tube persisting beneath skin of the postanal pit as an ependyma-lined cleft
• Rests:
  • can exhibit myxopapillary features
  • should not be construed as neoplastic by sole virtue of this growth pattern9

Gross Pathology

• Surgical exploration:
  • typically:
    • highly vascularized
    • ovoid or sausage-shaped mass
  • may be invested by fibrous pseudocapsule derived from stroma of filum
  • advanced examples may:
    • envelop cauda equina
    • erode neighboring bony structures
    • infiltrate paraspinal soft tissues
• Gelatinous appearance on sectioning
• Many show hemorrhagic discoloration.

Histopathology

• Usually instantly recognizable
• Cuboidal tumor cells:
  • drape about basophilic mucinous material that collars stromal blood vessels and collects in microcystic spaces (Fig. 1
    

    Fig. 1: Myxopapillary ependymoma. Note the manner in which mucinous material separates draping tumor cells from a hyalinized vascular core and accumulates in rounded microcysts.

    )
• Often spindly elements:
  • may engage in formation of gliovascular pseudorosettes
• ‘Giant cell’ ependymoma arising in filum terminale may contain conventional myxopapillary components10
• Sometimes:
  • eosinophilic spherules (‘balloons’):
    • possibly representing amalgamated collagen fibrils
  • myxoid matrix components
  • basal lamina materials1
• Common degenerative alterations include:
  • vascular sclerosis
  • hemorrhage
  • hemosiderin deposition
• Longstanding cases:
  • sometimes:
    • extensive fibrous tissue overgrowth
    • virtual obliteration of neoplastic cellular elements
• Ultrastructurally:
  • similar to other ependymomas, but:
    • less conspicuous cilia and microvilli
    • consistently elaborate basal lamina material that may invest cells as continuous basement membrane
    • may contain unique and specific ultrastructural marker of microtubules aggregated within cisternae of rough endoplasmic reticulum11

Special Stains and Immunohistochemistry

• Characteristic immunophenotype:
  • coexpression of:
    • vimentin
    • S-100 protein
    • GFAP
  • do not elaborate:
    • EMA
    • chromogranin
    • carcinoembryonic antigen (CEA)
  • exhibit little if any labeling for:
    • CAM 5.2
    • CK7
    • CK20

Diagnosis

Other Investigations

• Neuroimaging:
  • usually sharply delimited contrast-enhancing mass

Differential Diagnosis

Management

• Generally amenable to surgical cure:
  • recur and progress more frequently if amenable only to subtotal resection rather than complete removal
• Prolonged postoperative surveillance needed:
  • 15% experience late recurrences an average 5.8 years after excision

Prognosis

• Indolent
• 6.5% die of disease after repeated local recurrences over 12–15 years1
• Prognosis not altered by:
  • cytologic atypism
  • modest mitotic activity