The pathogenesis of epidermoid implantation cysts

The pathogenesis of epidermoid implantation cysts Bill R. Baker, D.D.S., :Il.X.D.,* Indianapolis, Id. INDIANA

UNIVERSITY

SCHOOL

cd

LIarGcl E’. Iliitchcll,

D.D.S., Ph.D.,“”

OF DEXTIYTKY

T

he behavior of rests and remnant,s of epithelium buried in the soft and hard tissues of the head and neck is receiving more and more attention as more pathologic entities of this region are identified. Keratin and fluid-filled cysts have been recognized for many years, but there is much still to be learned about their origin and mode of development. One type of cyst reported is the traumatic implantation cyst in the formation of which it is believed that a piece of surface t:pit,helium is implanted into (lceper tissues by accident or during a surgical procedure and then develops into a cyst in a manner which has been the subject of some conjecture for the past 100 years. The present study was designed to show the csact, changes in such dermal grafts from the time of implantation to the formation of corn plctc cysts. Also, in anticipation of future studies of cysts, it seemed useful to develop a simple and reproducible method for espcrimcntally producing such cyst,s in laboratory animals. REVIEW

OF THE LITERATURE

The earliest report, recognizing the implantation cyst was made 1)~ \Vcrnher,l who excised a “nut-sized tumor” from the palm of a thresher. The first expcrimcntal cysts wore produced in 3884 by Schwcningcr,2 who buried pieces of skin in the subcutaneous tissue of dogs, and by Kauffman,:’ who implanted cocks’ combs. Eriggs” reported an cpidcrmoid cyst of the finger in of Laboratory These experiments were conducted according to the “Principles of the National Society for Medical Research. views expressed herein are those of the authors and do not necessarily . The . op~nlons of the Knited States Air Force or the ljepartment of Defense. *Major, TJSAF (IX:), at prehent Chief of Oral Diagnosis, USAF Hospital (:hanute Air Force Base, Jll. Department of Oral Diagnosis/Oral Medicilte, **Professor and Chairman, University School of Dentistry.

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1X95. The same year Sutton” rcfcrred to this phenomenon as an “implantation cyst. ” In 1905 Pels-Leusden,” using a sharp knife to prevent implantation of epithelium, buried magnesium discs in the dermis of rabbits. Ultimately these tliscs were found to be surrounded by epithelium which he bclievcd to have originated from damaged dcrmal appendicular epithclium. H~ssc,~ in 1912, thought the cystic epithelium might have originated from hair follicles and glandular epithelium without any apparent burial of epidermis. L:y implanting full-thickness skin into the abdominal muscles of dogs, Davis and Trout” l)t.otluccd tubes and sacs lined with epithelium. Ewing” emphasized the prcdilect,ion of these cysts for occurrence in sites of frequent injury. (‘omprehcnsive csperiments with dogs were carried out by Zimches,l” who came to the following conclusions : (1) The epidermis forms a horseshoe and the ends meet on about the twenty-fifth day; (2) the cavity of the cyst is filled with epithelial debris and bits of hair; (3) the cyst grows through pressure of the build-up of cornified epithelium in the lumen; (4) small cysts may develop from the epithelium of hair follicles; (5) t,he tendency of surfncc clpithelium to bend on itself follows general laws of epithelial growth; (6) tnetaplasia was not seen; (7) the implanted section heals and joins its SLUrounding tissue by granulation tissue which later organizes into connective tissue. Peer and Paddock’l produced cysts in experimental animals in 1937. Later I’ecP reported the effects of burying skin grafts in human beings. He believed that the cysts developed but later disappeared in human beings. Strahan,‘” in 1950, reported that of 413 cases of hernial repairs using whole-skin grafts, nine failed because of the formation of cysts. Rutter” reported cyst formation 7 years following a cutis graft repair of hernia. He thought that tight suturing, to keep the graft from folding, might prevent cyst formation. IIuman experimental work was reported in 1957 by Epstein and Kligman,‘” who buried palmar and scalp epithelium in the corium of the scalp. Cyst formation was preceded by sloughing of the implanted epidermis, which was replaced by rpithelium streaming out of the hair follicles. The excellent photomicrographs in their report show sloughing not of the entire thickness of the stratified squamous epithelium but only about halfway through the prickle-ccl1 layer. Epstein and Kligman also emphasized that inflammation plays an inhibitory role in cyst forma.tion. In 1958 Gregory and Shafer? presented four cases of ciliated cysts of the maxilla. In each case a Caldwell-Luc sinus operation had been pcrformctl from 10 to 20 years previously. Gregory and Shafer suggested that these cysts were derived from bits of antral lining entrapped at, the site of incision. EXPERIMENTAL

PROCEDURE

Forty adult male Wistar rats, each weighing from 160 to 260 grams, were divided into ten groups of four and marked. Pentobarbital sodium, 3 mg. per 100 grams of body weight, was injected intraperitoneall-. The hair of the back was removed. Three 1.5 cm. horizontal incisions were made through the full skin t,hickness. A section measuring approximately 2 by 2 by 10 mm.

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6 0.1’.

.\ 14,

The WdU

Fig. 2. A 2-day graft. This graft rectangle is the area sho~~n in Fig. Iced +&,.)

has been folded 2. (Hematoxylin

in a cGL” and eosin

Pig. b. A S-day graft. Notice the distance of the epithelial arrt WY. Pieces of keratin may be seen free in the host connective rosi n stain. Magnification, ~100; reduced Ho.)

1C)Ci.i

autl rotatc~l 180 deg:1 -ees. stain. Magnification, >6% :

proliferation marked tissue. (Hematoxylin

I by and

\vas trimulcd from I hv cbdgc of this incision, invcbrtv(l, and implant,c(l thvollgh the incision into t,hp loose connective tissue 1 rltl. cephalad. Jt, was not possible 1c) orient all graft,s in the invcrl cbtl c~stcntlod position drsirccl. Thv incisions wcrc sutured. A l)ilot study had illtlicatctl that a coml)lete cyst could bc espccted in 2 weeks. so it was dtcided t,o kill one group of animals on postoperative days 2, 2, 4, 5, 6. 7, 9, 11, 13, and 15. Wide excision revealed the grafts adherent to the inner surface of the removed tissue. This tissue was fixed, trimmed perpendicular to the surface, and sections (7 microns) w(‘rc sta,incd with hcmatosylin and eosin. Serial sections were prepared of some specimens. RESULTS

None of the cysts that developed during this espcriment produced significant gross lesions in the allimals. Observable results were apparent only at, the microscopic l~vcl. Two-day

specimens

Xear the cut surfaces of the graft, the inflammatory response was mild in the host tissue. The capillaries appeared dilated, there was some margination of leukocytes, and a few polymorphonuclear leukocytes were to be seen free in the connective tissue. This inflammatory response was greatly increased in the tissue adjacent to the skin surface of t,he implanted tissue. Free keratin flakes were seen, surrounded by cells with large nuclei which appeared to be histiocytes. Because of the folding of the twelve grafts, forty-six sections of incised epithelial borders were available for examination. In thirty-four of these, proliferation was seen. In each case the proliferating margin was folding back against the connective tissue opposing the skin surface (Figs. 1 and 2). In some casesthis proliferation had proceeded as far as 0.6 mm. The proliferating epithelium was generally one or two cells in thickness. Three-day

specimens

The inflammatory changes were similar to the above, but in addition grannlation tissue was forming in the host tissue adjacent to the skin surface of the graft. Approximately 80 per cent of the incised epithelial borders were proliferating, all in the rctroverted direction described in the earlier specimens. Four-day

specimens

The band of granulation tissue was thicker. The twelve specimens showed further retroverting growth of the epithelium at the borders. Nany areas of proliferation were acanthotic. In one specimen, the two proliferating ends of epithelium had joined, forming a complet,e epithelium-lined cavity. Some of the specimens exhibited suprabasilar cleavage of the epithelium of the skin of the graft. In most areas this splitting was within the prickle-cell layer, but in a few areas basal cells were separated from the connective tissue. There were many dilated capillaries in the bases of the grafts. The graft having the greatest inflammatory infiltrate had the least epithelial proliferation.

Five-day

specimens

Several of the proliferating epithelial margins had met to form capsts. ‘l’hr lumina contained keratin and inAammat,ory cells. The inflammatory cells in the granulation tissue were about equally divided bet,ween pol~n~or~)hont~cle~~~ granulocytes and lymphocytes. There mere many giant cells in the granulai ion tissue. Six-day

specimens

One specimen had been sloughed. In the others the epithelium was prolifcrating and had closed, forming cysts in several cases. Some hair follicles appeared to be joining to form “microcysts.” Inflammation was less evident than in earlier groups (Fig. 3). Seven-day

specimens

A number of round basophilic bodies were seen in the Iumina of the forming cysts. Van Kossa staining did not bear out the impression that, they were calcified. At the margjns of the grafts endothelial proliferation was prominent, as vividly dcmonstratcd by the serial scctions just beyond t,he graft. Nine-day

with

specimens

The lnmina of some of these cysts were apparently the microcysts of hair follicle origin (Fig. 4).

enlarging

by ~onfl~~n~c

and not in the inverted position. Fig. 9. A B-day graft approximately 1 cm. in length, The retroverting proliferating epithelium has reached the arrows. Suprabasilar cleavage of the epithelium of the surface of the graft and acanthosis of the proliferating epithelium aw evidrnt in this section. (Hematoxylin and eosin stain. Magnification, ~35; rr~tlwrtl ;.$,.j

E‘ig. 4. A g-day graft. This origir: Iat,ing from the hair follicles stain. Maguification, x50 ; reduced

‘i.q. 5. 9 75day blium within thr stain. Mxguitiration,

graft. lumen

specimen illustrates the apparent fusiou of the with the lumen of a complete cyst. (Hrmatosyliu f&j.)

Rotice the relationship of the cyst to tllca skin x50; rcvlucrcl l/l,,.)

micrw *ysts autl clOSill

of the sloughed surface layers surfarc, of the grafts. (Trcnlni0sylilr

of t11r ant1

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specimens

Not all the graft,s had formed complete cysts, hat all showed rc~truvcrt i 11: proliferation from the incised epithelium. Thirteen-day

specimens

One of the grafts had been sloughed. IZpithelial proliferation with some complete cysts and some nearly complete ones. Fifteen-day

was cvidcnl,

specimens

Most of the sections now presented a closed cavit,y lined with epithelium. 111 the remainder, the proliferat,ion had proceeded to the point where closure was imminent. The specimen sectioned serially demonstrated an intact epitheliumlined cyst. The cysts at this period contained varying ratios of keratin to a protein-based fluid (Fig. 5). DISCUSSION

This project has followed the course of implanted autogenous skin grafts, noting the retroverting proliferation of the incised epithelial borders. These proliferating borders joined, thus forming a cyst. The proliferation of the incised epithelium should be reasonably expected, but it is more difficult to explain the invariable retroverting direction. The possibility that this growth follows planes of least resistance must be considered, but the loose relationship of the graft to the surrounding tissue seemsto make other possibilities equally plausible. This is particularly true of proliferation along the incised connective tissue of the graft. Although this appears to be the path most easily available for the formation of new epithelium, that phenomenon occurred in one case only. In this case retroverting proliferation occurred from the same border. Converse and Ballantynel’ have shown the dermal graft, to have a poor vascular bed for the first few days. This bed is replaced later by the ingrowth of new capillaries from the surrounding tissue. The proliferating epit,helium must have a good nut,rient supply and cannot at first obtain it from the avascular connective tissue of the graft. The direction of epithelial spread then may be determined by the availability of adequate nutrition from the host connective tissue surrounding the graft. The successof this simple method of implantation of autogenous epithelium to form cysts suggests a method for future st,udies of cyst development, enlargcmerit, and treatment. It would be of interest to implant epithelium from thn oral mucosa, ducts, sinuses, salivary glands, and tooth germs to observe the activity of epithelial tissues which have followed different paths of differentiation. SUMMARY

The purpose of this study was to record the changes in implanted skin leading IO epidermoid cyst formation. A total of’ 120 grafts of autogenous skin, each nlcasnring approximately 2 1)~ 2 by 10 mm., were implanted subcutaneously in corty male Wistar rats. Animals were killed at various intervals until 15 days had eln~~tl. Early- implants had ;m inflanll~l;ltor\~ rcac+on in thr surrounding

tissue, especially that opposite the keratinized surface. Two days after surgical intervention epithelial proliferation was seen at the incised borders of the implanted grafts. These proliferating sheets folded back on the keratinized surface of the implant, in some cases joining in a few days. After 5 days several of the epithelinm-lined cavities were seen. At this interval many hair follicles had lost their contents and had increased in size. Later these follicles apparently joined the lumina of the larger cysts. With the exception of two skin implants which sloughed, random and serial sections of the 5- to 15-day specimens showed some complete and some incomplete elongated cystic cavities filled with keratin, hair, and other debris. REFERENCES

1. Wernher, A.: Das Atherom, ein eingebalgtes Epitheliom, Virchows Arch. path. Anat. 8: 221. 1855. 2. Hchweninger, E.: Beitrag zur experimentellen Erzuegung van Hautgexchwulsten ( htheromen), Charit&Ann. 11: 642, 1884. 3. Kauffman, E.: fiber Enkatarrhaphie von Epithel, Virchows Arch. path. Anat. 97: 236, 18X4. 1. Briggs, F. M.: Two Cases of Cyst of the Finger, Boston 21. & Rurg. J. 133: 7, 1895. 5. Sutton. 5. B.: Implantation cvsts. Brit. M. J. 1: 461. 1895. 6. Pels-Leusden, F-: iiber abnorr;le Epithelisierung und traumatisehe Epithelcysten, Deutsche med. Wchnschr. 31: 1340, 1905. 7. Hesse, F. A.: Die Entstehung der traumatischen Epithelcpsten, Beitr. klin. Chir. 80: 494, 1912. S. ])a-&, J. S., and Trout H. F.: The Production of Epithelial Lined Tubes and Sacs, ;r. ii. M. A. 86: 339, 192d. 9. Ewing, J.: Neoplastic Diseases, ed. 3, Philadelphia, 1928, W. B. Saunders Company, 1). 1020. 10. iimches J. I,.: The Fate of Surface Epithelium Transplanted Into Deeper Tissues and Tts RelLtion to Epithelial Cysts, Frankfurt Ztschr. Path. 42: 203, 1931. 11. Peer, L. A., and Paddock: R.: Histologic Studies on Ihe Fate of Deeply Implanted Thermal Grafts. Arch. Sure. 34: 26X. 1937. 12. Peer, L. A:: Fite of B&&l Skin