Neurosurgery notes/Tumours/Pineal tumours/Desmoplastic myxoid tumour of the pineal region, SMARCB1-mutant

Desmoplastic myxoid tumour of the pineal region, SMARCB1-mutant

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Pineal tumours

General

  • Desmoplastic myxoid tumour of the pineal region, SMARCB1-mutant, is a rare, recently recognized tumour characterized by desmoplasia and myxoid changes while lacking traditional histopathological signs of malignancy.
  • It is defined by alterations of the SMARCB1 region on chromosome 22q11.

Definition

  • Essential criteria
    • A tumour in the pineal region that demonstrates both desmoplastic and myxoid features. AND
    • Lack of traditional histopathological signs of malignancy. AND
    • Loss of nuclear SMARCB1 expression.
  • For unresolved or difficult cases, a DNA methylation profile aligned with this entity is an essential criterion.

Numbers

  • This is an exceptionally rare tumour, with only 7 cases reported in the literature to date.
  • The median age at diagnosis is 40 years, with a range of 15 to 61 years reported.
  • The sex distribution appears nearly equal, with 4 female and 3 male patients identified so far.

Grade

  • A specific CNS WHO grade has not yet been assigned to this provisional entity.
  • Grading criteria remain to be defined, though its biological behaviour is thought to be less aggressive than that of atypical teratoid/rhabdoid tumour.

Histopathology

Microscopic

  • The tumour is characterized by an admixture of variably dense cords of small to medium-sized oval to spindled and epithelioid cells.
  • These cells are embedded within a heavily collagenized matrix and a loose, pale basophilic myxoid matrix.
  • Growth patterns may include fascicular or whorling arrangements.
  • Blood vessels within the tumour are frequently irregularly shaped, elongated, and show marked fibrosis.
  • Scattered rhabdoid cells are rare, and mitotic activity is exceptional, usually less than 1 mitosis per square millimetre.
  • The Ki-67 proliferation index is typically low, with a reported median of 3 per cent.
(A) Tumour cells embedded in loose, pale basophilic myxoid matrix with dispersed heavily collagenized material. (B) Small to medium-sized oval to spindled and epithelioid cells.
(A) Tumour cells embedded in loose, pale basophilic myxoid matrix with dispersed heavily collagenized material.
(B) Small to medium-sized oval to spindled and epithelioid cells.

Immunophenotype

  • The defining feature is the loss of nuclear SMARCB1 (INI1) expression.
  • Neoplastic cells often show expression of CD34 and EMA.

Genetic features

  • The tumour is driven by genetic alterations affecting the SMARCB1 region on chromosome 22q11.
  • Other chromosomal alterations are rare and do not appear to be recurrent.
  • On DNA methylation profiling, these tumours form a distinct group located near the AT/RT-MYC molecular subgroup and poorly differentiated chordoma.

Localisation

  • All cases reported to date have been localised within the pineal region.

Clinical presentation

  • Compression of pineal s(x)
    • Cerebral aqueduct:
      • Obstruction HCP
        • Papilledema
        • H/A
        • Ataxia
        • Impaired vision
        • N/V
    • Brain stem
      • Tectal plate compression: Parinaud syndrome
        • Loss of upward gaze
    • Cerebellum
      • Dizziness
      • Tremor
  • Endocrine
    • Diabetes insipidus
      • Present with DI because it infiltrates the floor of 3rd ventricle affecting the pituitary
    • Precocious puberty
  • Acute clinical presentation can be due to tumour apoplectic

Radiological features

  • Specific radiological findings for this entity are not detailed in the sources, but clinical data suggest it mimics other pineal parenchymal tumours.
  • Such masses are typically well-delineated and contrast-enhancing on MRI.
  • They are often hypointense or isointense on T1-weighted images and hyperintense on T2-weighted images.

Management

  • Surgical resection is the primary management strategy, with gross total resection achieved in the majority of reported cases.

Prognosis

  • Due to the limited number of cases, the long-term clinical course is not yet fully established.
  • Among the 7 known patients, after a median follow-up of 48 months, 3 were alive with stable disease, 1 experienced progression, and 3 had died from the disease.
  • No evidence of metastatic disease has been reported in any patient thus far.