Meningioma in a 9-year-old chocolate Lab: Anatomic pathology perspective
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, The University of Tennessee, Knoxville, Tennessee
Dr. Jennie Jankovsky provides the anatomic pathology perspective on this challenging oncology case.
Dr. Jennie JankovskyCanine meningiomas, which arise from the meninges, are generally solitary masses located within the rostral and basilar regions of the calvarium or over the cerebral convexities (Figures 4 and 5), with other locations occasionally noted.1
Figure 4. Meningioma (arrow) within the frontal lobe of another patient.
Figure 5. Meningioma (arrow) arising within the olfactory lobe region of another patient.
Intravertebral and orbital meningiomas are also infrequently reported (Figure 6).2,3 Grossly, these masses are firm, broad-based, well-circumscribed, ovoid to plaque-like, and have a smooth to granular surface. Metastasis is rarely reported to the lungs.4-6
Figure 6. Meningioma (arrow) in the cervical spine of another patient.
The current World Health Organization (WHO) veterinary histological classification system divides meningiomas into benign and anaplastic (malignant) groups. The benign category is further characterized by histologic pattern, including meningothelial, fibrous, transitional, psammomatous, angiomatous, papillary and granular types.7 Meningothelial and transitional forms are most common in dogs.8,9
A grading system and additional histologic patterns are included within the WHO classification scheme for human meningiomas.10 Canine and human meningiomas are similar histologically, so evaluation of canine meningiomas with the human classification scheme allows greater prognostic capability.9 The WHO grading system for human meningiomas consists of three grades: benign (grade I), atypical (grade II), and malignant (grade III). Benign tumors lack histologic indicators of malignancy and include all histologic subtypes except clear cell, chordoid, papillary and rhabdoid. Atypical meningiomas are characterized by ≥ 4 mitoses/10 hpf, possible brain invasion, and three out of five of the following criteria:
• Cells arranged in sheets
• High nuclear to cytoplasmic ratio
Additionally, clear cell and chordoid variants are included in the atypical category. Malignant meningiomas have ≥ 20 mitoses/10 hpf, features of malignancy similar to those described for atypical masses, and, if anaplastic, may resemble other neoplasms, such as carcinoma, sarcoma or melanosarcoma. The papillary and rhabdoid subtypes are included within the grade III category.10
Immunohistochemistry may be used to differentiate anaplastic meningiomas from other intracalvarial neoplasms. Meningiomas are immunoreactive to vimentin, CD34, E-cadherin, and doublecortin, with variable positivity for S-100, claudin-1, and neuron specific enolase (NSE).11-13 Neoplastic cells are not immunoreactive to synaptophysin, but are occasionally positive for cytokeratin and glial fibrillary acidic protein (GFAP), although often weakly or in a low percentage of cells.11,12
In the current case, histologic features were most consistent with a grade I meningothelial meningioma (Figures 7 and 8). Neoplastic cells had mild anisocytosis and anisokaryosis, with 3 mitoses/10 hpf. Necrosis and brain invasion were not present within the tissues examined.
Figure 7. Meningothelial meningioma from the dog in this case. Epithelioid cells are arranged in sheets and loose whorls (hematoxylin and eosin stain; 100x).
Figure 8. Meningothelial meningioma from the dog in this case. There are mitoses (arrows) (hematoxylin and eosin stain; 400x).
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9. Sturges BK, Dickinson PJ, Bollen AW, et al. Magnetic resonance imaging and histological classification of intracranial meningiomas in 112 dogs. J Vet Intern Med 2008;22:586-595.
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11. Barnhart KF, Wojcieszyn J, Storts RW. Immunohistochemical staining patterns of canine meningiomas and correlation with published immunophenotypes. Vet Pathol 2002;39:311-321.
12. Ramos-Vara JA, Miller MA, Gilbreath E, et al. Immunohistochemical detection of CD34, E-cadherin, claudin-1, glucose transporter 1, laminin, and protein gene product 9.5 in 28 canine and 8 feline meningiomas. Vet Pathol 2010;47:725-737.
13. Ide T, Uchida K, Suzuki K, et al. Expression of cell adhesion molecules and doublecortin in canine anaplastic meningiomas. Vet Pathol 2011;48:292-301.