Schwannoma

From Dog
Histological appearance of a schwannoma with bone differentiation[1]

Schwannoma are an infiltrative peripheral nerve sheath tumor similar to neurofibroma, and characterized by benign neoplastic Schwann cells (normally produce the insulating myelin sheath covering peripheral nerves). In dogs, these tumors may present as either benign or malignant.

Although schwannomas are entirely formed of neoplastic Schwann cells, neurofibromas are a mixture of Schwann cells, perineurial cells and fibroblasts[2][3], with the Schwann cell the primary neoplastic cell[4].

A collective term 'benign peripheral nerve cell tumor' has been advocated instead of schwannoma or neurofibroma due to the close histological appearance of these two tumor types as well as both benign schwannomas and benign neurofibromas behave similarly in clinical setting[5].

Schwannomas are most frequently associated with cranial nerve VIII (acoustic or vestibulocochlear nerve)[6] but extradural (spinal column and brachial plexus)[7][8], intracranial[9], testicular[10] and malignant epithelial schwannomas[11] have been reported.

Affected dogs often present with ipsilateral forelimb lameness, neck pain, head tilt, episodic circling or difficulty opening the mouth[12].

Secondary hypertrophic osteoarthropathy[13] and erythrocytosis have been reported.

Diagnosis is based on presenting clinical history, and needle biopsy or tissue biopsy during surgical excision.

These tumors have an infiltrative growth, with a characteristic microscopic appearance of spindle-shaped neoplastic cells arranged in sheets and concentric whorls. They may exhibit different morphological patterns, specifically Antoni type A where spindle cells are arranged in palisades and Antoni type B which are less cellular and organized, made of oval to round loosely arranged cells.

Many heterogeneous patterns have been described such as epithelioid, rhabdomyoblastic, cartilaginous, osseous, angiomatous, glandular and lipoblastic[14].

Definitive diagnosis usually requires immunohistochemical staining for S-100 antigen, neuron-specific enolase, and glial fibrillary acidic protein[15][16]. S-100 antigen staining appears to be selective with benign schwannomas[17].

A differential diagnosis would include hemangiopericytoma, vestibular disease, metastatic lymphoma, osteosarcoma and masticatory muscle myositis.

Initial improvement may be noted with use of prednisolone[18], presumably due to resolution of mass-effect edema, but treatment usually requires surgical removal.

Recurrence with schwannomas is common[19], although survival times greater than 3 years have been reported post-operatively[20].

References

  1. Viott, AM et al (2008) Schwannoma with bone differentiation in a dog. Braz J Vet Pathol 1(2):52 - 55
  2. Skovronsky DM & Oberholtzer JC (2004) Pathologic classification of peripheral nerve tumors. Neurosurg Clin N Am 15:157–166
  3. Megahed M (1994) Histopathological variants of neurofibroma: a study of 114 lesions. Am J Dermatopathol 16:486–495
  4. Gottfried ON et al (2006) Molecular, genetic, and cellular pathogenesis of neurofibromas and surgical implications. Neurosurgery 58:1–16
  5. Gross TL et al (2005) Mesenchymal neoplasms and other tumors. In: Skin Disease in the Dog and Cat, ed. GrossTL, Ihrke PJ,WalderEJ, and Affolter VK, 2nd ed., pp. 786–796. Blackwell Science, Oxford, UK
  6. Koestner A & Higgins RJ (2002) Peripheral nerve sheath tumors. In: Tumors in domestic animals, ed. Meuten DJ, 4th ed., pp:731–735. Iowa State Press, Ames, IA
  7. Bradney IW & Forsyth WM (1986) A schwannoma causing cervical spinal cord compression in a dog. Aust Vet J 63(11):374-375
  8. Uchida K et al (1993) Malignant schwannoma in the spinal root of a dog. J Vet Med Sci 54(4):809-811
  9. Summers B et al (1995) Neoplasia and the peripheral nervous system. In: Veterinary neuropathology, ed. Duncan L, pp:472–501. Mosby Year-book, St. Louis, MO
  10. Rothwell TL et al (1986) Schwannoma in the testis of a dog. Vet Pathol 23(5):629-631
  11. Pumarola M et al (1996) Malignant epithelioid schwannoma affecting the trigeminal nerve of a dog. Vet Pathol 33(4):434-436
  12. Cizinauskas S et al (2001) Paradoxical vestibular disease with trigeminal nerve-sheath tumor in a dog. Schweiz Arch Tierheilkd 143(8):419-425
  13. Hara Y et al 91995) Regression of hypertrophic osteopathy following removal of intrathoracic neoplasia derived from vagus nerve in a dog. J Vet Med Sci 57(1):133-135
  14. Plaza JA et al (2006) Lipoblastic nerve sheath tumors report of a distinctive variant of neural soft tissue neoplasm with adipocytic differentiation. Am J Sur Pathol 30:331-344
  15. Ottinger T et al (2009) Malignant acoustic schwannoma in a dog. J Vet Diagn Invest 21(1):129-132
  16. Gaitero L et al (2008) Canine cutaneous spindle cell tumours with features of peripheral nerve sheath tumours: a histopathological and immunohistochemical study. J Comp Pathol 139(1):16-23
  17. Seppälä MT & Haltia MJ (1993) Spinal malignant nerve-sheath tumor or cellular schwannoma? A striking difference in prognosis. J Neurosurg 79(4):528-532
  18. Saunders JH et al (1998) Probable trigeminal nerve schwannoma in a dog. Vet Radiol Ultrasound 39(6):539-542
  19. Yamauchi A et al (2004) Secondary erythrocytosis associated with schwannoma in a dog. J Vet Med Sci 66(12):1605-1608
  20. Bailey CS (1990) Long-term survival after surgical excision of a schwannoma of the sixth cervical spinal nerve in a dog. J Am Vet Med Assoc 196(5):754-756