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Pilomatricoma
(PILOMATRIXOMA, NECROTIZING AND CALCIFYING EPITHELIOMA OF MALHERBE)
A benign tumor showing exclusively matrical differentiation.
Gross Appearance:
•Elevated, intradermal skin mass
•Varies in size from 1-6 cm in diameter
•May ulcerate or show alopecia
•White chalky appearance on cut section
•May be multilobulated and pigmented
•Often difficult to transect due to bone within the tumor
Histology:
•One or more lobules separated by a collagenous stroma
•At the periphery is a zone of basophilic cells
•Have small hyperchromatic nuclei and little cytoplasm
•May show moderate mitotic activity
•Abrupt transition to the central zone of shadow or ghost cells
•Cells have a central clear area, remnants of the cell nucleus and eosinophilic cytoplasm
•Multinucleated giant cells and proliferating fibroblasts
•Some tumors show calcification and ossification
•Endstage tumors have few basophilic cells at the periphery
Prognosis:
Good; seldom recur following surgical excision. Occasional cases of malignat pilomatrixoma with lymph node and lung
metastasis may be found
| Breeds At Increased Risk |
| Breed |
Odds Ratio |
95% Confidence Limit |
Probability |
| Kerry Blue Terrier |
61.190 |
45.813 - 81.729 |
0.001 |
| Bouvier des Flandres |
12.394 |
7.215 - 21.292 |
0.001 |
| Soft Coated Wheaton Terrier |
12.094 |
7.591 - 19.269 |
0.001 |
| Standard Poodle |
11.788 |
9.370 - 14.829 |
0.001 |
| Old English Sheepdog |
9.503 |
6.758 - 13.363 |
0.001 |
| Irish Wolfhound |
7.671 |
3.605 - 16.325 |
0.001 |
| Airedale Terrier |
7.129 |
4.795 - 10.600 |
0.001 |
| Bichon Frise |
6.851 |
4.585 - 10.131 |
0.001 |
| Puli |
6.789 |
1.665 - 27.690 |
0.037 |
| Bearded Collie |
6.710 |
2.128 - 21.158 |
0.011 |
| West Highland White Terrier |
4.448 |
3.058 - 6.469 |
0.001 |
| Border Collie |
2.991 |
1.235 - 7.244 |
0.029 |
| Basset Hound |
2.936 |
1.878 - 4.591 |
0.001 |
| Miniature Poodle |
2.871 |
2.187 - 3.768 |
0.001 |
| Standard Schnauzer |
2.853 |
1.734 - 4.696 |
0.001 |
| Miniature Schnauzer |
2.428 |
1.650 - 3.573 |
0.001 |
| Maltese |
2.400 |
1.136 - 5.070 |
0.030 |
| Shih Tzu |
1.813 |
1.134 - 2.899 |
0.024 |
| Lhasa Apso |
1.810 |
1.083 - 3.024 |
0.034 |
| Breeds At Decreased Risk |
| Breed |
Odds Ratio |
95% Confidence Limit |
Probability |
| Golden Retriever |
0.454 |
0.299 - 0.688 |
0.001 |
| Mixed Breed |
0.431 |
0.345 - 0.538 |
0.001 |
| Beagle |
0.341 |
0.141 - 0.822 |
0.007 |
| German Shepherd |
0.311 |
0.166 - 0.581 |
0.001 |
| Labrador Retriever |
0.248 |
0.143 - 0.429 |
0.001 |
| Cocker Spaniel |
0.187 |
0.084 - 0.417 |
0.001 |
| Husky |
0.182 |
0.045 - 0.731 |
0.003 |
| Dachshund |
0.104 |
0.015 - 0.738 |
0.002 |
| Rottweiler |
0.070 |
0.010 - 0.498 |
0.001 |
| Boxer |
0.057 |
0.008 - 0.407 |
0.001 |
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Sex Distribution (N=701)
|
| Sex |
Status |
Percent
|
|
|
|
28.2 |
|
|
17.8 |
|
|
|
24.0 |
|
|
30.0 |
(normal sex distribution)
| Anatomic Location (N=644) |
| Site |
Percent
|
| Hindlimb |
19.9 |
| Back |
15.4 |
| Thorax |
14.0 |
| Neck |
12.0 |
| Forelimb |
11.3 |
| Abdomen |
10.4 |
| Tail |
9.8 |
| Multiple |
3.4 |
| Head |
3.1 |
| Perineum |
0.7 |
| 
