I. G. Renn,ie
Pathological examinationMacroscopic appearances. The lesion was
describedas a ruptured cyst measuring 5 mm in diameter.
Microscopic examination. Histologically the cystwall was
composed of granular, intensely eosino-philic cuboidal cells
forming a papillary-tubularstructure. Occasional cells contained
large brownishgranules in their cytoplasm. These granules did
notstain by any silver impregnation technique andwere considered to
be lipofuscin granules. Scantymucus-secreting cells were present
throughout thelesion. There was little nuclear pleomorphism,
andmitotic figures were not identified in the sectionsstudied. A
scanty condensation of connective tissuesurrounded the lesion.
Discussion
The term oncocyte was devised by Hamperl15 todescribe an
epithelial cell that was characterised byits large size and
eosinophilic granular cytoplasm.The derivation of the term (Greek:
Onkausthui-toswell) was thought by Hamperl to convey theessential
morphological characteristic of the cell,namely its large swollen
appearance. Electronmicroscopic studies5 16-18 (and case 1 of this
report)have since shown that the essential feature of thesecells is
the number of mitochondria within thecytoplasm. It is believed that
the increase in mito-chondria in the oncocyte reflects a defect of
meta-bolism in this organelle leading to a compensatoryincrease in
their number.19 Though the primarymetabolic defect is not known, it
is thought to arisein old 'burnt out' cells, a concept inferred
from theincreasing incidence on oncocytic lesions with age.
Benign oncocytomas arising in ocular adnexahave been described
in the lacrimal gland, lacrimalsac, plica semilunaris, bulbar
conjunctiva, upperand lower fornices, mucocutaneous junction,
andlacrimal caruncle. Of these, the caruncular oncocy-toma is by
far the commonest; however, even inthis site it is a rarity. In a
study of 200 lesionsarising from the caruncle Evans20 described
only 1case which may have been an oncocytoma, theprecise
histological details being unavailable. Sincethat report probably
only 25 cases (excluding thisreport) have been
described.Oncocytomas are generally regarded as benign
tumours. However, sporadic reports of malignantoncocytomas have
appeared. Malignant oncocy-tomas of the parotid have been
described.2' 23 Onecase arising from a gland in the nasal mucosa
hasalso been described.'9 Four malignant oncocytomasarising in
ocular adnexa have been described, 2arising in the lacrimal sac24
25 and 2 occurring in thelacrimal gland.626 In relation to the
lacrimal gland
only 1 benign oncocytoma has been described.27 Itis surprising
that so few lacrimal oncocytomas(benign or malignant) have been
described, espe-cially when one considers the fact that
oncocyticmetaplasia is known to occur in this organ. Bockand
Schlagenhauff'8 examined the lacrimal glandsof 20 necropsies and
found oncocytic metaplasia in7 of them (35%). Equally surprising is
the apparentexcess of malignant tumours to benign lesions. Itis
possible to attribute these anomalies to the extre-mely slow growth
of the benign oncocytoma.Case 3 above illustrates the extremely
slow
growth of this tumour. The lesion was present forat least 7
years before excision. Thus benign lacrimaloncocytomas may never
attain sufficient size tocause symptoms and thus escape detection.
Incontrast, a malignant lesion with its more rapidgrowth and
invasion of adjacent tissues would beexpected to produce
symptoms.
HISTOGENESIS OF CARUNCULARONCOCYTOMASThe histogenesis of the
caruncular oncocytoma isstill open to discussion. Anatomically the
lacrimalcaruncle is a piece of modified skin. It is covered
bystratified squamous epithelium and contains hairfollicles,
sebaceous glands, and sweat glands. Itdiffers from skin in that it
contains accessory lacri-mal glands similar to those of
Krause.These glands are usually in the centre of the
caruncle and open by a sinuous duct near the plicasemilunaris.29
Three possible sites of origin areproposed-the surface epithelium,
the conjunctiva,and the accessory lacrimal glands. Other
suggestedsites of origin such as sweat glands2 or mucousglands'3
seem improbable, for oncocytomas are notdescribed arising from
these structures in othersites.The accessory lacrimal glands or
ducts have
been proposed as the site of origin by severalauthors' 2 5 6
10-12 in view of their histologicalappearances (see below). Greer8
described 2 casesof caruncular oncocytoma which appeared to
arisefrom the surface epithelium. Case 2 above similarlyshowed
close apposition to the surface epithelium.However, in this example
oncocytic metaplasia waspresent in the duct of an accessory
lacrimal glandpresent near the tumour, though a direct
continua-tion between the 2 could not be demonstrated.Forbes and
Crawford" described a case in which adilated secretory duct
displaying oncocytic meta-plasia was in direct continuity with an
oncocytoma.A possible explanation for the existance of a lesionin
apparent continuity with the surface epitheliumas described by
Greer8 and the author (case 2) isthat the lesion could have arisen
from the epithelium
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Onicocytomas (oxyphil adetiomas) of iic lacrimalcarlncle9
of a secretory duct immediately beneath the carun-cular
epithelium. Briggs and Font6 described focaloncocytic metaplasia in
the ducts and acini ofaccessory lacrimal glands present in the
region ofthe caruncle. Radnot and Lapis5 examined anoncocytoma with
the transmission electron micro-scope and found, particularly at
the periphery ofthe lesion, epithelial cells morphologically
identicalto those of accessory lacrimal glands. It wouldseem
unlikely that oncocytomas arise from thecaruncular epithelium
proper, as this is a stratifiedsquamous epithelium similar to skin,
and, so far asthe author is aware, oncocytomas have not
beendescribed arising from cutaneous structures else-where in the
body.
It is possible that caruncular oncocytomas arisefrom the
conjunctiva immediately adjacent to thecaruncle. In support of this
argument Briggs andFont6 described 2 oncocytomas apparently
arisingfrom the bulbar conjunctiva near the plica semi-lunaris. If
oncocytomas were to arise mainly fromthe conjunctiva, then one
should anticipate oncocy-tic changes described more frequently in
the con-junctival epithelium, but this is not the case. More-over,
in relation to lesions described arising fromthe plica semilunaris,
it is to be noted that this isthe site of drainage of the secretory
duct of thecaruncular lacrimal tissue. It would appear that
themajority, if not all, caruncular oncocytomas arisefrom accessory
lacrimal glands or their secretoryducts. This belief is supported
by the similar histo-logical appearances of oncocytomas occurring
atthe caruncle and thoEe occurring in other secretoryglands, namely
the major salivary glands.
CLINICAL ASPECTSTo the clinician the caruncular oncocytoma is
ararity. Nevertheless the diagnosis should be con-sidered when he
sees a caruncular swelling, particu-larly if the lesion appears
cystic or has a brightcherry red colour. The lesion appears to
occurmainly in postmenopausal females. In the 28 casesrecorded,
including this report, 5 patients have beenmale (in one case the
sex of the patient was notgiven), a ratio of 5 6:1 females to
males. It usuallyhas an extremely slow rate of growth and
oftenpresents as a chance finding.
The author thanks Miss M. A. C. Jones and Mr C. A. L.Palmer for
allowing the publication of their clinical material;Professor L.
Henry and Mr A. Stanworth for their help andencouragement; Miss F.
Bishop and Mrs S. Porter for theirassistance with the technical
preparation of the specimens.
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