Neurofibroma

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Plexiform neurofibroma in the colon of a dog. Diffuse ganglioneuromatosis is apparent (asterisk)[1]

Neurofibroma and neurofibrosarcoma are an infiltrative benign peripheral nerve sheath tumor, classified as a differentiated form of Schwannomas which can affect both the peripheral and central nerve tissue[2].

Although schwannomas are entirely formed of neoplastic Schwann cells, neurofibromas are a mixture of Schwann cells, perineurial cells and fibroblasts[3][4], with the Schwann cell the primary neoplastic cell[5].

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[6].

Neurofibrosarcomas are frequently located in the cerebrum[7], intestines[8] and heart[9], whereas neurofibromas are often located in the subcutis, peripheral nerves, tongue or large intestine.

Clinically affected dogs usually present with a slow-growing tumor, often affecting nerve-rich tissues such as the ovaries[10], .

Blood tests and imaging studies (radiographs, ultrasonography and MRI) are usually unrewarding.

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

Neurofibromas are usually single, well-demarcated, expansile tumors, but a plexiform variant has been reported that is composed of multiple nodular masses[1].

Histological examination of neurofibromas usually reveals three common forms; localized, diffuse and plexiform types. Macroscopically, these tumors are frequently composed of well demarcated multinodular masses with centrally located nerve fiber bundles surrounded by neoplastic nerve sheath tissue. Microscopically, these tumors can appear as classic, cellular, collagenous, myxoid, and pigmented forms, with slender, elongated cells containing buckled and/or wavy nuclei in a fibromyxoid stroma with thin, wire-like collagen fibers. Within the mass, nerve fibers can be identified.

Immunohistochemistry usually reveals positive staining limited to neoplastic Schwann cells[11].

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

Treatment of subcutaneous neurofibromas usually involves surgical extirpation of the tumor. Chemotherapy with cisplatin has shown good responses[12].

References

  1. 1.0 1.1 Schöniger S & Summers BA (2009) Localized, plexiform, diffuse, and other variants of neurofibroma in 12 dogs, 2 horses, and a chicken. Vet Pathol 46(5):904-915
  2. Scott DW & Miller WH (2003) Neoplastic and non-neoplastic tumors. In: Equine Dermatology, ed. Scott DW and Miller WH, pp. 698–795. WB Saunders, St. Louis, MO
  3. Skovronsky DM & Oberholtzer JC (2004) Pathologic classification of peripheral nerve tumors. Neurosurg Clin N Am 15:157–166
  4. Megahed M (1994) Histopathological variants of neurofibroma: a study of 114 lesions. Am J Dermatopathol 16:486–495
  5. Gottfried ON et al (2006) Molecular, genetic, and cellular pathogenesis of neurofibromas and surgical implications. Neurosurgery 58:1–16
  6. 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
  7. Platt SR et al (2002) Comparison of fine-needle aspiration and surgical-tissue biopsy in the diagnosis of canine brain tumors. Vet Surg 31(1):65-69
  8. LaRock RG & Ginn PE (1997) Immunohistochemical staining characteristics of canine gastrointestinal stromal tumors. Vet Pathol 34(4):303-311
  9. Aupperle H et al (2007) Primary and secondary heart tumours in dogs and cats. J Comp Pathol 136(1):18-26
  10. Sontas BH et al (2010) Vaginal neurofibroma in a hysterectomized poodle dog. Reprod Domest Anim 45(6):1130-1133
  11. Fletcher CD (2007) Peripheral neuroectodermal tumors. In: Diagnostic Histopathology of Tumors, ed. Fletcher CDM, 3rd ed., pp. 1733–1762. Churchill Livingstone, Elsevier, Philadelphia, PA
  12. Tozon N et al (2001) Electrochemotherapy: potentiation of local antitumour effectiveness of cisplatin in dogs and cats. Anticancer Res 21(4A):2483-2488
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