Postgradutate Medical Journal (December 1980) 56, 823-827

Epidermal cysts - a clinicopathological and biochemical studyV. CHANDRASEKARAN*

M.S.SATYA PARKASH*

F.R.C.S. (Eng.)

C. V. RAGHUVEERtM.D., D.C.P.

Departments of *Surgery and tPathology,Jawaharlal Institute of Postgraduate Medical Education and Research,

Pondicherry 605006, India

SummaryThe findings of a clinicopathological and biochemicalstudy of epidermal cysts and a review of the relevantliterature are presented. A punctum was found in 40%of 34 epidermal cysts that were studied in detail. Thefindings of the histological study were in favour of thepunctum being the orifice of an obstructed hair folliclefrom which at least a proportion of the epidermalcysts are likely to develop. The biochemical analysisof the contents of the cysts revealed a very low proteinand lipid content, thus ruling out any 'sebaceous'contribution. Bacteriological study of clinically in-flamed cysts showed that inflammation in these lesionswas usually aseptic unless there was a communicationbetween the cyst cavity and the exterior.

IntroductionSebaceous cyst is the most common diagnosis

offered whenever a cystic lesion of the skin is en-countered in surgical practice. As the contents ofthese lesions appear to be sebaceous on casualexamination, it was for long presumed that theselesions resulted from blockage of the sebaceousducts with the consequent retention of the sebaceoussecretion. Although work published by pathologistsand dermatologists has disproved this theory beyondall doubt, surgical text books, by and large, con-tinue to use this term and subscribe to this dis-credited theory. As a result, much confusion andmisconception exist among surgeons regarding thetrue nature of these lesions. This study was under-taken, therefore, in an attempt to study thesecommoncystic lesions by correlating their clinical character-istics with the underlying pathology and the bio-chemical nature of their contents.Although it is not clear as to when exactly the

term 'sebaceous cyst' came into use, the 'sebaceousconcept' could be traced to the great pathologist

Rudolf Virchow, who considered all epithelium-lined cysts of the skin with semi-solid or fluid con-tents to be formed from sebaceous glands (Warviand Gates, 1943). The term 'sebaceous cyst' has beenused to describe most, if not all, cystic lesions of theskin. However, as far back as 1930, Broders andWilson classified these lesions on the basis of histo-logy and physical characteristics of their contentsinto 'keratomas' and true sebaceous cysts. In 1943,Warvi and Gates and Love and Montgomery madeseparate studies and arrived at similar conclusionsalthough they preferred to call the 'keratomas' ofBroders and Wilson as 'epidermal cysts' and 'epi-thelial cysts' respectively. Kligman in 1964 studied13 of the so-called sebaceous cysts and concludedthat they were nothing more than a variety ofkeratinous cyst. McGavran and Binnington (1966)made a detailed study of all the characteristics of'sebaceous cysts' including their histochemicalreactivity and mode of keratinization, as observedunder the electron microscope. They concludedthat the keratinous cysts, wherein keratinizationoccurred without keratohyaline granules, as in thecases of the cortex of hair and nail, were derivedfrom the piliary apparatus, particularly the externalroot sheath and hence should be called 'pilar cysts'.In contrast to this, they found that keratinization inthe more generally distributed epidermal cystsoccurred with the formation of keratohyalinegranules as in the case of epidermis. Nicoloides,Leven and Fu (1968) analysed the lipid pattern ofepidermal and the so-called sebaceous cysts andfound that neither of them resembled the lipidpattern of the sebaceous gland secretions. Pinkus(1969), while accepting the pilar theory, identifiedthe follicular isthmus of the external root sheath ofthe hair follicle as the exact origin of these pilarcysts and suggested the name 'trichilemmal cysts'.

0032-5473/80/1200-0823 $02.00 (CO 1980 The Fellowship of Postgraduate Medicine

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824 V. Chandrasekaran, S. Parkash and C. V. Raghuveer

Thus, at present it is fairly clear that, except forsteatocystoma multiplex, a rare and inherited dis-order, there are 2 main types of skin cyst, the epi-dermal and the pilar, in place of the non-existent'sebaceous cyst'. While the origin of pilar cyst isnow well understood, the histogenesis of the epi-dermal cyst is still not clear. Various theories havebeen postulated from time to time. Sebaceous ducts(Broders and Wilson, 1930), rudimentary cell rests(Love and Montgomery, 1943), pluripotent epi-thelial systems of epidermis (Kligman, 1964) andoccluded pilosebaceous follicle (Aurora and Blodi,1972; Caro, 1975), have all been suggested as thestructures of origin. Implantation dermoids, whichare a variety of epidermal cyst, are generally con-sidered to be caused by trauma, either blunt orpenetrating (Epstein and Kligman, 1957; Sandersonand Machie, 1979).

Materials and methodsA clinico-pathological study of all the cases of

epidermal and pilar cysts subjected to histology dur-ing the period January 1978 to September 1979 wasmade from the Institute Hospital records. Of these,34 consecutive epidermal cysts and one pilar cystwere subjected to a critical study which included adetailed clinical examination, a histological studyand a biochemical analysis of the contents for totalproteins and lipids. During the clinical examination,a special effort was made to find out the presence ofa punctum, using a magnifying glass (x 10) where-ever necessary. In the case of cysts having a punctum,3 to 5 serial sections at a distance of 3,u were madethrough the punctum. The sections were stainedwith haematoxylin and eosin and studied under themicroscope for the structure of the cyst wall, theappearance of the contents and the exact nature ofthe punctum. Estimation of total proteins (Biuretmethod) and lipids (Gravimetric method) in theundehydrated cyst contents was done in 15 epi-dermal cysts including 4 implantation dermoids.Five subcutaneous dermoids and 3 teratomatousdermoids containing a dermal element were alsosubjected to a similar biochemical study for com-parison. Only those cysts which had no clinical signsof inflammation and were removed with an intactcyst wall were accepted for biochemical analysis toexclude contamination with tissue fluids and blood.The content of the only pilar cyst studied could notbe biochemically analysed as it had burst and wasinflamed at the time of examination. The contents of4 inflamed epidermal cysts, one implanatation der-moid and on pilar cyst were also subjected to a bac-teriological culture.

ResultsDuring the study, 249 epidermal or 'sebaceous'

cysts were diagnosed at the surgical outpatient de-partment of the Jipmer Hospital, of which only 123cysts (41-8 %) were subjected to histological examin-ation. Out of these 123, 2 were pilar (1 58 %) and therest epidermal cysts.The 121 histologically proved epidermal cysts

were from 84 male and 37 female patients, a maleto female ratio of 2 : 1. The oldest patient was 70years old and the youngest 3 years (average, 29-3years). The highest incidence occurred in the 3rdand 4th decades. There was a wide variation induration from 3 months to 30 years (average, 3-2years). The commonest site was the face (19-0%)followed by the chest wall (12-41 %), thigh (10-74%),gluteal region (8-34 %) and scalp (8-26 %). The largestcyst (gluteal region) was 9 cm and the smallest(scrotum) was 0-5 cm. The lesions were mostlysingle except for scrotal cysts which were multiplelesions in all 5 cases.Of the 34 consecutive cysts studied in detail, 15

showed a punctum (42-1%). Face, back and thegluteal region were the most frequent sites. In all 15cases, the punctum was visible to the naked eye. Clini-cally it appeared as a small dark opening throughwhich the cyst contents could be squeezed out, or asa minute pit, where the skin was adherent to the

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FIG. 1. Epidermal cyst with punctum (arrowed)

underlying cyst (Figs 1 and 2). Six of 34 cysts(17-6%) had histological evidence of inflammation.Of these, only 5 were clinically inflamed. Two casesof multiple cysts of the scrotum had clinical evidenceof calcification; and one cyst occurring in the cheekhad microscopical evidence of calcification, givingan overall incidence of calcification of 8-8 %.Both cases of pilar cyst occurred on the scalp of

women. Of these, only one, in a 50-year-old woman,was studied in detail: it was 3 cm in size and was of

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Epidermal cysts 825

30 years' duration. The patient had, while combingher hair, accidentally traumatized the cyst one weekbefore examination. At the time of examination thecyst was collapsed, tender and was dischargingscanty, thick yellowish fluid through a raggedopening near its base.

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FIG. 2. Punctum (arrowed) as seen in the cut section of twoepidermal cysts.

Of 121 cases of epidermal cysts 10 were cystsoccurring in the recognized site of implantationdermoids namely the palms, fingers and soles andcould be classified as implantation dermoids - anincidence of 83 % (8 male and 2 female patients):all but one of the men were manual labourers; nonegave a history of antecedent trauma. While 6 cystsoccurred in the fingers, one each occurred in thepalm and the inter-digital cleft and 2 in the soles.Significantly only one of the 6 cysts seen in thefingers was situated in the finger tip, the site mostcommonly exposed to trauma. Similarly both thecysts occurring in the soles were also situated innon-weight-bearing areas, namely the medial aspectof the ball of the great toe and the web space. Twoof the implantation dermoids had evidence ofinflammation.On histological examination, all the epidermal

cysts including the implantation dermoids werefound to have an epidermal lining with a distinctgranular cell layer and laminated keratin materialforming the content. The lining was of variablethickness and the cells appeared to become flattenedas they moved towards the cyst cavity (Fig. 3). Oneof the cysts had a portion of disintegrated hair shaftin the cyst cavity. In contrast to this, the pilar cystsshowed a lining composed of several layers of paleepithelial cells with indistinct cell outlines. The cellsappeared to become swollen as they moved towards

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the cavity, changing abruptly into an amorphouskeratin without the formation of a granular celllayer (Fig. 4). In the case of inflamed cysts, therewere one or more breaches in the cyst wall where theepidermal lining was replaced by inflammatory cells.Extensive calcification of the cyst cavity could be

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FIG. 4. Pilar cyst showing typical lining (HE, x 100).

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FIG. 5. Punctum seen as an opening, through which the cystlining is continuous with the surface epidermis (HE, x 100).

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826 V. Chandrasekaran, S. Parkash and C. V. Raghuveer

seen in the 2 cases of multiple epidermal cyst of thescrotum studied in detail. The epidermal lining wasmarkedly attenuated and barely discernible atplaces.Of the 15 cysts subjected to serial sections, the punc-

tum could be demonstrated in 4 and less distinctly inone. In 3 of these the punctum appeared to be aminute opening through which the epidermal liningof the cyst wall appeared to be continuous with thesurface epidermis (Fig. 5). In the other cases thepunctum was represented by an area of invaginationof the surface epidermis which appeared to be con-nected with the cyst wall lining. Arrectores pilorummuscle could be seen attached to this connection inat least one case (Fig. 6).

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FIG. 6. Punctum showing the connection between the surfaceepidermis and the cyst lining and the arrectores pilorummuscle.

The biochemical examination revealed 0-49, 0-54,0-88 and 0-85 g % of protein; and 0-97, 0-74, 0-96,and 1-28 g % of lipids in the content of epidermalcysts, implantation dermoids, sequestration der-moids and teratomatous dermoids respectively.The contents of all the 4 clinically inflamed epi-

dermal cysts and one implantation dermoid werefound to be sterile on bacteriological culture, butthe one pilar cyst grew Klebsiella sp.

DiscussionEpidermal cysts are said to have an equal inci-

dence among the sexes. The significant male pre-dominance seen in this study perhaps reflects thereluctance of women of Pondicherry to seek medicalhelp for this simple lesion. This may also be thereason for the comparatively low incidence of pilarcysts which are known to occur predominantly inwomen (Caro, 1975). Contrary to the observationsof Leppard, Sanderson and Wells (1977a) and

Sanderson and Machie (1979), there was no evidenceof an autosomal dominant type of inheritance inthe 2 cases studied.There were certain special clinical features in the

5 cases of epidermal cyst of the scrotum in the pres-ent study which, so far as the authors know, havenot been stressed in the literature: all 5 cases were ofvery long duration (10-30 years) and had multiplecalcified lesions which were arranged symmetricallyalong the midline raphae in distribution though notin size. In the case of implantation dermoids,absence of a history of antecedent trauma and theirpresence in areas least exposed to trauma indicatethat the theory of traumatic origin is not entirelysatisfactory although trauma may be an excitingfactor in a few cases.Although it has long been known that a punctum

is seen only in a proportion of epidermal cysts (Loveand Montgomery, 1943), there is no mention in theliterature of its exact incidence. As for its histologicalpicture, in 2 cases it was seen as an invagination ofthe surface epidermis connected to the cyst walllining. That arrectores pilorum muscle was attachedto this connection is strong evidence that the punc-tum here actually represents the orifice of theobstructed hair follicle. It is possible that this repre-sents an earlier stage in the development of a punc-tum. The other 3 cases where the punctum was seenas an opening connecting the cyst cavity with theexterior probably represent a later stage, where theincreasing pressure in the cyst cavity may have'reopened' the obstructed pilosebaceous canal. Whatcauses the initial obstruction of hair follicles whicheventually distends to form a cyst, is a matter forspeculation. Keratotic plugging (Auroroa and Blodi,1972) seems a reasonable explanation in some ofthese cases. That one of the cysts showed a piece ofdisintegrated hair shaft in the cyst cavity appears tocorroborate this view. However, it may also beargued that the gross stretching of a vicinity hairfollicle may, in some cases, lead to follicle atrophyand a patulous opening overlying the cyst whichresembles a punctum.The very low lipid and protein contents indicate

that there is no sebaceous contribution to the cystcontent which is essentially composed of epithelialdebris and keratin and is no different from similarmaterial occurring elsewhere such as the sub-preputial collection (Parkash et al., 1973). Thatbacteria could be isolated only from the one rup-tured pilar cyst accords with the view of Leppard,Thomson and Noble (1977b) that inflammation inthese cysts is usually an aseptic one caused by thecyst contents coming into contact with the sur-rounding tissues unless there is a communicationwith the exterior, when bacterial contamination canoccur.

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Epidermal cysts 827

ReferencesAURORA, A. L. & BLODI, F. C. (1972) Benign epithelial cysts

of the eyelids. In: Current Concepts in Ophthalmology,Vol. III (Ed by Blodi, F. C.), p. 206. The C. V. MosbyCompany, Saint Louis.

BRODERS, A. C. & WILSON, R. (1930) Keratoma - a lesionoften mistaken for sebaceous cyst. Surgical Clinics ofNoth America, 10, 127.

CARO, W. A. (1975) Epithelial cysts. In: Dermatology Vol. 2(Ed by Moschella, S. L., Pillsbury, D. M. & Hurley, H. J.),2nd Edn, p. 1329. Saunders Company, Philadelphia,London and Toronto.

EPSTEIN, W. L. & KLIGMAN, A. N. (1957) Epithelial cysts inburied human skin. Archives of Dermatologv, 76, 437.

KLIGMAN, A. N. (1964) The myth of the sebaceous cyst.Archives of Dermatology, 89, 253.

LEPPARD, B. J., SANDERSON, K. V. & WELLS, R. S. (1977a)Hereditary tricholemmal cysts. Clinical and ExperimentalDermatology, 2, 25.

LEPPARD, B. J., THOMSON, J. P. S. & NOBLE, W. C. (1977b)

Bacteriology of skin cysts. British Journal of Dermatology,96, 511.

LOVE, W. R. & MONTGOMERY, H. (1943) Epithelial cysts.Archives o' Dermatology and Syphilology, 47, 185.

MCGAVRAN, M. H. & BINNINGTON, B. (1966) Keratinouscysts of skin. Archives of Dermatology, 94, 499.

NICOLOIDES, N., LEVEN, N. E. & Fu, H. C. (1968) The lipidpattern of the wen. Journal of Investigative Dermatology,50, 189.

PARKASH, S., JEYAKUMAR, S., SUBRAMANYAN, S. & CHAUDHRI,S. (1973) Human subpreputial collection - its nature andformation. Journal of Urology, 110, 211.

PINKUS, H. (1969) 'Sebaceous cysts' are trichilemmal cysts.Archives of Dermatology, 99, 544.

SANDERSON, K. V. & MACHIE, R. (1979) Cysts of the skin.In: Text Book of Dermatology (Ed by Rook, A.,Wilkinson, D. S. & Ebling, F. J. G.), 3rd edn, Vol. 2,p. 2158. Blackwell Scientific Publications, Oxford, London,Edinburgh and Melbourne.

WARVI, W. N. & GATES, 0. (1943) Epithelial cysts and cysttumors of the skin. American Journal of Pathology, 19, 765.

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