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

 

               Sex Distribution (N=701)

Sex Status

Percent

Male

(45.0%)

46%
intact

(28.1%)

 28.2
neutered

(16.9%)

 17.8
Female

(55.0%)

54%
intact

(23.9%)

 24.0
neutered

(31.1%)

 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


Copyright © 2000 - University of Pennsylvania School of Veterinary Medicine
Faculty: Michael H. Goldschmidt, BVMS & Patricia Mcmanus,VMD, PhD
Student: Kyle Goldschmidt
Comments: goldsch@vet.upenn.edu