Hair follicles in the canine tongue Ernest A. Swanson, Jr., Ph.D., Philadelphia, DEPARTMENT
SCIENCES, TEMPLE UNIVERSITY
SCHOOL OF DENTISTRY
At least three normal-appearing and mature hair follicles containing hairs were found to be growing in a coiled manner within the intrinsic musculature of the anterior two thirds of a dog’s tongue. An extensive review of the literature has shown that hair follicles are, indeed, found in some unusual places, but previous finding of their presence in the tongue has not been reported. Microscopic examination of serial sections failed to produce any evidence that these follicles were the result of some form of foreign body accident or teratomatous process. They appeared histologically normal in all respects and are assumed to be endogenous to the tongue. The embryologic development of these follicles is briefly commented upon.
A lthough the presence of hair follicles and hairs in teratomas is a fairly routine finding,’ their existence in otherwise ectopic locations is a chance observation. An extensive review of the literature has shown that hair follicles are found in some strange places. Doyen* reported finding hairs in marrow spacesand in liver parenchyma. Schinckel” observed hair follicles growing on the amnion of a sheep. In 1960, Miles” reported a single case of an isolated hair follicle growing in human cheek mucosa. A second case of human oral hair has recently been reported by Baughman and Heidrich.” Their specimen was found growing from the attached mandibular gingiva of a 45-year-old man. Previous finding of the presence of hair follicles in the tongue, however, has not been mentioned in the literature. MATERIALS
A portion of the anterior two thirds of a normal and healthy dog’s tongue was processedthrough our histology laboratory for use as microscopic teaching specimens for a course in oral histology for dental students. The tongue was routinely dehydrated and embedded in paraffin. Five-micron serial cross sections were cut and stained with hematoxylin and eosin. More than 300 microscopic slides were produced and examined. Since the slides were meant solely for teaching, the technician retained only the better slides and no attempt was made to keep the slides in absolute serial order. At a later date, when hair follicles were discovered in the tissue, the advantage of studying them from serial sections became obvious, but by that time the remainder of the original specimen had been discarded. An effort was made to reassemble the prepared slides into a 0030-4220/81/030277
04%00.40/O 1981The C. V. Mosby Co.
semblance of serial order by microscopic observation and grouping; however, this turned into a task of herculean proportions, and very little information was gained from the attempt. RESULTS
At least four normal-appearing and mature hair follicles containing hairs were found. In all cases they were closer to the dorsal surface of the tongue than to the ventral surface (Figs. 1 through 6). In most instances the follicles were found within skeletal muscle fascicles of the intrinsic tongue musculature (Figs. 1, 2, 4, and 6). Occasionally they were seenin the lamina propria of the dorsal surface (Fig. 3) or deeper within the substance of the tongue, where they were in close association with both skeletal muscle and irregularly arranged dense collagenous connective tissue (Fig. 6). None of the follicles observed was seen to possess associated sebaceousglands or arrector pili muscles. Likewise, there were no adnexal sweat glands in the vicinity of the hair follicles. Frequently the striated muscle fibers of the tongue were seen to blend with the collagen fibers surrounding the follicles, suggestive of an insertion of muscle into the sheath of the follicle (Fig. 5). One section of the dorsal surface of the tongue demonstrated what appeared to be an emerging hair shaft, but owing to the absence of serial sections, direct continuity with any of the underlying follicles could not be demonstrated. In each of the follicles containing hair shafts, the morphology of the hair itself (cortex, medulla, and cuticle) appeared normal (Figs. 5 and 6). Likewise, the cellular morphology of the outer root sheaths of the follicles appeared normal (Fig. 6). One follicle that possessed a well-formed germinal matrix 277
Oral Surg. March, 1981
Fig. 1. Histologic cross section from the body of a dog’s tongue showing the dorsal surface. Typical filiform papillae are in the upper part of the photograph. The arrows indicate cross sections of a hair follicle embedded within muscle fascicles of longitudinalis linguae superior. (Hematoxylin and eosin stain. Magnification X 50.) Fig. 2. Histologic section approximately 2 mm. distal to the area shown in Fig. 1. Arrows indicate cross sections of hair follicle believed to be the same as those in Fig. 1. Arrowhead indicates a follicle profile in longitudinal-oblique section and embedded between skeletal muscle fibers of verticalis linguae. (Hema-
toxylin and eosin stain. Magnification, X 50.) Fig. 3. Another follicle in cross section some distance removed from the group illustrated in Figs. 1 and 2. Cortex and medulla of hair shaft are plainly visible. (Hematoxylin and eosin stain. Magnification,
x 50.) Fig. 4. AITOWS show two cross-sectioned profiles of hair follicle different from those in Figs. 1 and 2. (Hematoxylin and eosin stain. Magnification, x 50.)
enclosing a normal-appearing connective tissue papilla was found. Each slide was carefully searched for evidence of acute or chronic inflammation in the area of the hair follicles. None was found. The dorsal and ventral surfaces were both examined for evidence of scar formation or any microscopic sign
of a previous injury, but again nothing There were no tumors present.
In observing various groups of follicle profiles from different areas of the tongue, the definite
Hair follicles in canine tongue
Fig. 5. High magnification of the same hair follicle shown in the upper part of Fig. 4. Medulla, cortex, and the darkened cuticle of the hair shaft can be seen. (Hematoxylin and eosin stain. Magnification, x 125.) Fig. 6. Oblique section through hair follicle showing normal-appearing stratum spinosum-like cells of the external root sheath. Note skeletal muscle fibers of the intrinsic tongue musculature in the left part of the photograph. (Hematoxylin and eosin stain. Magnification, x 125.)
impression was gained that the follicles were coiled as opposed to growing straight down, as is normally Seen in skin bearing hair follicles. This fact can be appreciated by comparing Figs. 1 and 2. The two sections were approximately 1 to 2 mm. apart. The two cross-sectioned profiles are presumed to be the same follicle, and the presence of the longitudinaloblique profile in Fig. 2, if also the same follicle, gives the impression of coiling of the entire structure. The absence of any evidence of infection or inflammation in the area of the follicles, combined with the lack of scar formation in the vicinity, seems to rule out the possiblility of some type of foreign body injury to the tongue which might account for the hairs. Also, the fact that the follicles appear histologically normal leads to the conclusion that they are truly endogenous to the tongue in this specimen and not the result of a teratomatous process. It is to be remembered that the anterior two thirds or body of the tongue is clothed with an epithelium that was originally stomodeal ectoderm.’ In view of this, it is probably not surprising to find hair follicles here; nor is it difficult to envision them growing down into the underlying musculature. Embryologically speaking, the primary requirements for the differentiation of ectoderm with ensuing formation of hair follicles and hairs are the presence of an
inductive stimulus from the mesoderm and the competence of the ectoderm to react to that stimulus.” In the present case, both of these prerequisites were met, and yet, owing to the apparent rarity of the phenomenon, either or both must usually be absent in the tongue. It must also be remembered that certain mammals (for example, Rodentia) have hairy skin as part of the lining of the inner surface of the cheek. Since this condition is not assumed to occur in the remote ancestors of canines, their chance observation in the dog’s tongue is unlikely therefore to have any phylogenetic significance. On a priori grounds, it appears that the hair follicles observed here arose as a simple aberration of development in fetal or early embryonic life. It has been demonstrated, however, that, even late in life, sebeceous glands may develop in portions of the oral mucosa previously devoid of them.“. i The possibility also exists that the hair follicles observed in the tongue may have developed at some time long after the birth of the animal. Thanks are extended to Miss Helen Ruane for preparing the slides and to Mrs. Margaret Pickard for typing the manuscript. REFERENCES
1. Corliss, C. E.: Patten’s Human Embryology, New York, 1976, McGraw-Hill Book Company,Inc. 2. Doyon: Migration de pails dans les canaux osseuxet Ie
3. 4. 5. 6.
parenchyme hepatique. Conditions du phenomene, Arch. Anat. Micr. 25: 395404. 1929. Schinckel, P. G.: Competence of the Amniotic Ectoderm to Differentiate in Sheep:Nature 194: 1261-1262, 1962. Miles. A. E. W.: A Hair Follicle in Human Cheek Mucosa, Proc. ‘R. Sot. Med. 53: 527-528, 1960. Baughman, R. A., and Heidrich, P. D.: The Oral Hair: An Extremely Rare Phenomenon, ORAL SURG. 49: 530-531, 1980. Miles, A. E. W.: Sebaceous Glands in the Lip and Cheek Mucosa of Man, Br. Dent. J. 105: 235-248, 1958.
Oral Surg. March, 1981 7. Miles, A. E. W.: The Development and Atrophy of Buccal Sebaceous Glands in Man, J. Dent. Res. 37:757, 1958. Reprint requests to: Dr. Ernest A. Swanson, Jr. Department of Anatomic Sciences Temple University School of Dentistry 3223 North Broad St. Philadelphia, Pa. 19140