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Papillary Tumor of the Pineal Region (PTPR)

  • Background:
    • PTPR is a rare neuroepithelial tumor that arises from specialized ependymocites in the subcommissural organ, located in the posteroinferior wall of the third ventricle (pineal region).
    • Recognized neoplasm in the WHO 2007 classification; grading criterion has yet to be defined, but in the 2016 WHO, PTPR corresponds to grade II or III neoplasms.
    • Only a few PTPRs with imaging findings have been reported.
    • The immunohistochemical findings help differentiate PTPR from other lesions in the pineal region, such as pineal parenchymal tumor of intermediate differentiation (PPTID).
  • Clinical Presentation:
    • PTPR occurs in both children and adults, but most cases are seen in adults (mean age at diagnosis is 32 years).
    • PTPR can compress the tectum and cerebral aqueduct, causing hydrocephalus.
  • Key Diagnostic Features:
    • PTPRs tend to be large and lobulated, relatively not well circumscribed, and partially cystic.
    • MRI: T1WI variable signal intensity (intrinsic hyperintensity has been described); T2WI isointense or hyperintense and heterogeneous postcontrast enhancement; restricted diffusion on DWI
    • In such scenarios, it is necessary to screen the entire neuraxis to assess for CSF spread.
    • Radiologic findings are nonspecific in most patients. PTPRs are easily differentiated microscopically, showing distinct papillary architecture with pseudostratified columnar epithelium.
  • Differential Diagnoses:
    • PPTID: No radiologic features that would distinguish these tumors
    • Pineocytoma: Well-demarcated round or nodular masses; the imaging appearance is less “aggressive” than a PTPR. MRI: Iso-hypointense on T1WI, hyperintense on T2WI, and variable enhancement
    • Metastasis: Metastases to the pineal gland are rare (prevalence of 0.4%–3.8%), but may be present without metastases to brain parenchyma. Can be indistinguishable on imaging studies from primary pineal neoplasms.
    • Germinoma: More than 90% of patients are younger than 20 years at initial diagnosis. MRI: Iso-hyperintense on T2WI, with intense and homogeneous enhancement. Dissemination by CSF and invasion of the adjacent brain are also typical.
    • Brainstem astrocytoma with extension to the pineal region: Those that take place in the region of the tectum are usually low grade (WHO I–II) and occur more frequently in childhood. MRI: Bulbous enlargement of the tectal plate; isointense on T1WI and hyperintense on T2WI with no to minimal enhancement.
  • Treatment:
    • Surgical resection if it is possible
    • The clinical course of PTPR is characterized by frequent local recurrence.
    • The value of radiotherapy on disease progression in PTPR will need to be investigated in a future prospective trial, which will also provide data on long-term follow-up and may further aid the identification of histopathologic factors possibly associated with prognosis in PTPR.
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