J Clin Pathol 1982;35:1074-1077

Unusual subcutaneous mixed tumour exhibitingadipose, fibroblastic, and epithelial components

PS SMITH, J McCLURE

From the Division of Tissue Pathology, Institute of Medical and Veterinary Science, Frome Road, Adelaide,South Australia 5000

SUMMARY A subcutaneous mass in the left supraclavicular fossa of a 55-year-old woman provedon histological examination to be composed of islands of squamous cells embedded in bands ofspindle cells and associated with mature adipose tissue. Electron microscopy showed that thespindle cells were fibroblastic in nature and not squamous cells showing spindle differentiation.There was also a minor lymphangiomatous component and sparse infiltrates of lymphoid cells.The lesion bore certain similarities to thymolipoma except that the presence of spindle cells andthe site were atypical. While it may be speculated that the tumour was thymolipoma occurring in

an ectopic cervical thymus the lesion is provisionally regarded as an unusual mixed tumourfeaturing mesenchymal and epithelial components.

The histopathological examination of a subcutane-ous tumour removed from the left supraclavicularfossa revealed epithelial, fibroblastic, and matureadipose tissue components. Since descriptions of asimilar entity could not be found in previous reportsthe results of histopathological and ultrastructuralstudies of this lesion are reported here. The possibil-ity that the tumour represents an unusualthymolipoma occurring in an ectopic cervicalthymus is discussed as is the classification of thelesion in a group of tumours referred to as non-metastasising mixed tumours featuring adipose tissueand an epithelial component.

Case report

The patient was a 55-year-old woman who had beenin good health. She presented with a lump in the leftsupraclavicular region which had apparently beenpresent for many years and which had been growingslowly. A clinical diagnosis of lipoma was made andthe lump was excised. It was lateral to the ster-nomastoid muscle and deep to the platysma. It wasnot related to the thyroid gland. The mass shelledout easily although it did dip down behind the clavi-cle a little. There appeared to be no extension to thethoracic cavity and there were no significant attach-ments. The deep aspect of the tumour was superfi-

Accepted for publication 6 January 1982

cial to the muscles of the neck and superficial to thevessels in the root of the neck. Chest x-ray revealedno evidence of mediastinal enlargement.

PATHOLOGICAL FEATURESThe tumour was a well circumscribed ovoid massmeasuring 80 x 50 x 40 mm and weighing 85 5 g.The cut surface was transected by bands of pale tis-sue bounding areas of typical adipose tissue (Fig. 1).Microscopically there was a discrete fibrous capsule.There was an intimate mixture of disparate elements(Fig. 2). There was a background of mature adiposetissue in which there were islands and strands ofsquamous epithelium. Occasionally these were lyingfree in adipose tissue, or in loose connective tissue(Fig. 3) or surrounded by a sparse lymphoidinfiltrate (Fig. 4). The squamous cell componentsexhibited heratohyalin formation and occasionallycystic degeneration. Most frequently the islands ofsquamous cells lay in bands of spindle cells (Fig. 5)which transected the tumour and which corres-ponded to the bands of pale tissue seen macroscopi-cally. Another microscopic feature was a lymphan-giomatous component.

Portions of formalin-fixed tissue were post-fixedin osmium tetroxide and processed into Spurr'sresin. Survey sections were cut and representativeblocks were thin-sectioned for electron microscopy.There were islands of cells separated from a col-

lagen stroma by a basal lamina. These cells hadmildly irregular nuclei with occasional nucleoli and

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Unusual subcutaneous mixed tumour exhibiting adipose, fibroblastic and epithelial components

Fig. 1 Cut surface ofthe tumour showing adipose tissuetransected by bands ofpale tissue

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Fig. 3 Island ofsquamous epithelium (arrowed)embedded in loose connective tissue. Haematoxylin andeosin x 200

Fig. 4 Island ofsquamous epithelium (arrowed)surrounded by lymphocytes. Haematoxylin and eosin x200

Fig. 2 Adipose tissue admixed with bands ofspindle cells.There are squamous islands and a background vascularity.Haematoxylin and eosin x 120

their cytoplasm contained small amounts of roughendoplasmic reticulum (RER), mitochondria, freeribosomes and tonofilaments. Desmosomes werealso seen infrequently between cells (Fig. 6). In thestroma there were spindle-shaped cells with quitevariable nuclear morphology ranging from regular-ovoid to convoluted, and containing occasional nuc-leoli. Their cytoplasm contained moderate amountsof RER and small numbers of mitochondria and freeribosomes (Fig. 7). The mature lipocytes were alsoseen, their cytoplasm was filled with a single largelipid droplet.

Discussion

This is a most unusual tumour and a description of acorresponding lesion has not been found in previousreports. It is a mixed tumour with mesenchymal,squamous and lymphangiomatous elements butwithout chondroid, Schwann cell or other differenti-ation. The total clinical and macroscopic featuressuggest that it is a discrete fatty tumour rather than aneoplasm infiltrating normal fat. In the differentialdiagnosis one must consider a mixed tumour ofsalivary gland origin, a sweat gland tumour and lesslikely a peculiar variant of one of the mixed tumoursof the thyroid or parathyroid gland such aslipoadenoma of the parathyroid. Again theclinicoanatomical features of this case tend to ruleout the latter possibilities as well as salivary andsweat gland tumours. One is therefore left with a

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Fig. 5 Bands ofspindle cells (S) adjacent to matureadipose tissue (A). Haematoxylin and eosin x 200

tumour with a distinctive pattern of islands ofsquamous cells merging with spindle cells and set ina background of mature adipose tissue. The onlytumour in which a majority of these features hasbeen described is a thymolipoma. The presence of alymphangiomatous component is also consistentwith a thymolipoma since on one occasion several

Smith, McClure

foci of cystic lymphangiomatous tissue were presentin an otherwise typical thymolipoma.' Thymolipomais a comparatively rare tumour some 60 cases havingbeen reported2 and it is said to comprise between2% and 9% of all thymic tumours.3 The majority ofthe features exhibited by the present tumour wouldbe consistent with a thymolipoma except that thereis no available account of a spindle cell componentin thymolipomas. The site of the lesion is unusualand there would appear to be no continuity with themediastinum and neither is there evidence of a sepa-rate lesion in the mediastinum.

Ectopic thymic tissue may occur in the neck andthe lesion may therefore be thymolipoma in anectopic cervical thymus.The electron microscopic findings confirms the

presence of squamous cells (with desmosomes andtonofilaments) and mature lipocytes. The spindlecells did not contain desmosomes and tonofilaments.Their overall features were indicative of cells of afibroblastic nature and not squamous cells showingspindle differentiation. The differentiation of whiteadipose tissue has been described by Napolitano.4The presumptive precursors of lipoblasts are indis-tinguishable from fibroblasts in the earliest stage anddifferentiation takes place through early lipoblasticand midstage lipoblastic phases to mature lipocytes.Early and midstage lipoblasts were not seen in thepresent lesion and it is therefore unlikely that thespindle cells are presumptive lipoblasts.

This therefore is an unusual tumour. One canspeculate about its origin in an ectopic cervicalthymus but one cannot be categorical on this point.

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Fig. 6 Edge ofa squamous islandshowing collagenous stroma (C), amildly irregular nucleus (N),tonofdaments (single arrows), adesmosome (double arrows) andbasal lamina (triple arrows). x6400

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Utnusual suibcutatneous mixed tumour exhibiting adipose, fibroblastic and epithelial components

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The lesion is therefore best regarded as an unusualsubcutaneous mixed mesenchymal tumour featuringadipose tissue, a spindle cell component and anepithelial component. It was well encapsulated,easily excised and there was no significant cellularpleomorphism or mitotic activity. The lesion is con-sidered, on these grounds, to have a good prognosis.The lesion may be another member of a group of

neoplasms which are all rare and which havereceived little attention as a group. These are non-metastasising mixed mesenchymal tumours featur-ing adipose tissue and an epithelial component.5 Thetumours include thymolipoma, lipoadenoma of theparathyroid gland,6 thyrolipomal and mammaryadenolipoma. The latter is regarded by Azzopardi8as merely a lipoma which has incorporated lobularepithelial elements.The precise nature of this group of tumours must

be regarded as somewhat controversial. They maybe true neoplasms, hamartomas or less likely, rep-resent fatty degeneration in foci of parenchymatoushyperplasia. Probably the consensus of opinionwould be that thymolipoma is a true neoplasm but aresolution of the precise nature of the other entitiesmust await recognition and description of furtherexamples of these rare lesions.

We wish to thank Mrs L Murray and Miss R Noblewho cut the EM sections and Mrs C Wickremasuriyafor typing the manuscript.

References

Scully NM. Lipothymoma with cystic lymphangioma: case report.Ann Surg 1960;26:400-4.

2 Reintgen D, Fetter BF. Roses A, McCarty KS. Thymolipoma inassociation with myasthenia gravis. Arch Pathol Lab Med1 978; 102:463-6.

Rosai J. Levine GD. Tumours of the thymus. Washington DC:Armed Forces Institute of Pathology. 1976:162-6.

4 Napolitano L. The differentiation of white adipose cells. An elec-tron microscope study. J Cell Biol 1963;18:663-79.

Allen PW. Tumours and proliferations of adipose tissue: aclinicopathological approach. New York: Masson PublishingUSA Inc, 1981:75.

6 Abul-Haj SK, Conklin H, Hewitt WC. Functioning lipoadenomaof the parathyroid gland: report of a unique case. N Engl JMed 1962;266:121-3.

'Chesky VE, Dreese WC, Hellwig CA. Adenolipomatosis of thethyroid: a new type of goitre. Surgery 1953;34:38-45.

Azzopardi JG. Problems in breast pathology. London: WB Saun-ders Co Ltd, 1979:396.

Requests for reprints to: Dr J McClure, Institute of Medi-cal and Veterinary Science, PO Box 14, Rundle Street PostOffice, Adelaide, South Australia 5000.

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