Primitive neuroectodermal tumor

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Postmortem photograph of the left side of the occipital cortex, cerebellum, and brainstem of a 4-year-old Labrador Retriever with a tumor mass adherent to the underlying brainstem (arrow)[1]

Primitive neuroectoderm tumors (PNET) are a rare embryonal round cell brain tumor of dogs.

Embryonal tumors of the nervous system are rare in dogs, with the possible exception of medulloblastoma of the cerebellum, which is mostly seen in young dogs[2].

Forms of primitive ectodermal tumor include:

- Ganglioneuroma (benign)
- Neuroepithelioma (benign)
- Ganglioneuroblastoma (intermediate)
- Esthesioneuroblastoma (intermediate)
- Medulloblastoma (aggressive)
- Neuroblastoma (aggressive)
  • Medulloepithelioma

Several diagnostic entities have been grouped under the term 'primitive neuroectodermal tumors' to more accurately reflect the concept that a primitive neuroectodermal cell can differentiate in several directions, sometimes within the same tumor[3]. The term medulloblastoma has been retained to describe those tumors that arise from the external granular layer of the cerebellum[4].

Primitive neuroectodermal tumor is a good descriptive compromise for tumors arising from neuroectoderm that differentiate towards neurons and/or glial cells. These tumors are considered to be malignant, grow rapidly and may metastasize. They can be divided into central PNETs (arising from the brain or spinal cord) or peripheral PNETs (arising from neural tissue within bone or soft tissue[5].

Clinical symptoms are variable depending on tumor location. In one case, a 4-year-old Labrador Retriever presented with a 6-month history of weight loss, left-sided Horner's syndrome, left facial paresis, an occasional cough, inspiratory stridor and a change in phonation[1]. Other dogs freuqently present with ataxia, head tilt, strabismus, nystagmus and circling[6].

Magnetic resonance imaging of the brain showed the presence of a multilobulated mass in and around the left tympanic bulla that was also present in the vertebral canal and the cranial vault, where it compressed the proximal cervical spinal cord and the brainstem, respectively.

Diagnosis in most canine cases is determined at postmortem.

Immunohistochemically, these tumors stain positively with vimentin, triple neurofilament protein, neuron specific enolase and synaptophysin.

Treatment in most cases requires surgical debulking and adjunct radiation therapy. Chemotherapy is considered ineffective with these germ cell tumors.

References

  1. 1.0 1.1 Gains MJ et al (2011) A primitive neuroectodermal tumor with extension into the cranial vault in a dog. Can Vet J 52(11):1232-1236
  2. Koestner A & Higgins RJ (2002) Tumors of the nervous system. In: Meuten DJ, editor. Tumors in Domestic Animals. 4th ed. Ames, Iowa: Iowa State Univ Pr. pp:697–738
  3. Louis DN et al (2008) Tumours: Introduction and neuroepithelial tumours. In: Love S, Louis DN, Ellison DW, editors. Greenfield’s Neuropathology. 8th ed. London, UK: Edward Arnold; Pr. pp:1821–2000
  4. Summers BA et al (1995) Tumors of the central nervous system. In: Summers BA, Cummings JF, de Lahunta A, editors. Veterinary Neuropathology. St. Louis, Missouri: Mosby-Year Book. pp:351–401
  5. Mobley BC et al (2006) Peripheral primitive neuroectodermal tumor/Ewing’s sarcoma of the craniospinal vault: Case reports and review. Human Pathology 37:845–853
  6. Choi US et al (2012) Cytologic and immunohistochemical characterization of a primitive neuroectodermal tumor in the brain of a dog. Vet Clin Pathol 41(1):153-157