A Case of Neurilemoma (Schwannoma) That Mimicked a Pleomorphic Adenoma (An Example of Potential Pitfall in Aspiration Cytodiagnosis) Raj K. Gupta, M.D., FlAC and Carl s. Dowle M.B., Ch.B., FRACS

Needle-aspiration cytology of a case of benign neurilemoma (Schwannoma) from the neck is presented. It was clinically diag- nosed as an enlarged lymph node, while on aspiration cytology, it was diagnosed as a pleomorphic adenoma. A n excision biopsy, however, was diagnostic of neurilemoma. A review of cytologic material was undertaken, and it was felt that the cytologic fea- tures in Papanicolaou stained preparations in the aspirate were present that initially should have enabled the correct cytodiagnosis and distinction from a pleomorphic adenoma. The findings pre- sented in this study were considered to be an example of a poten- tial pitfall in the aspiration cytodiagnosis of a neurilemoma. Diagn Cytopathol 1991;7:622-624.

Key Words: Needle aspiration cytology; Head and neck; Schwan- noma; Adenoma

Solitary neurilemoma (Schwannoma) is a relatively un- common neoplasm and is believed to arise from the nerve sheath. 1,2 It can occur anywhere in the body, although a site of prediliction is the head and neck area. In recent years the recognition of this neoplasm in needle aspirates from various body sites has been documented in rare case reports. 3-8 This seems to enhance the value of needle aspi- ration cytology (NAC), which has more frequently been used in the diagnosis of epithelial tumours, and since neurilemoma is a soft-tissue tumour of mesenchymal deri- vation in which NAC has been used more recently. The problems in the diagnosis of mesenchymal tumours are known. Therefore it is not unusual that with the increas- ing application of NAC in cases of neurilemoma, a cytopa-

Received December 27, 1990. Accepted May 14, 1991. From the Departments of Cytology and Surgery, Wellington Hospital

Address reprint requests to Raj K. Gupta, M.D., FIAC, The Cytology and School of Medicine, Wellington, New Zealand.

Unit, Wellington Hospital, Wellington, New Zealand.

thologist may be called upon to interpret an aspirate prior to tissue examination. Rarely, the cytologic features may present diagnostic difficulties, especially if a mimicking pattern to another tumour is observed in an aspirate that has been taken from a lump in the head and neck region. lo

This communication describes such a case in which a palpable lump in the neck was clinically diagnosed as an enlarged lymph node, while cytologically it was diagnosed as a pleomorphic adenoma. A review of the aspirate, how- ever, did suggest features of a neurilemoma. These fea- tures are described and the potential pitfalls are presented. As far as we are aware, only one similar case has recently been described in the literature. lo

Case Report A 47-yr-old female presented with a 10-yr history of a lump on the right side of her neck. It was asymptomatic and in the last few weeks had slightly increased in size. No history of weight loss, fever, or night sweats was present, and the past history and family history were noncontribu- tory. On physical examination nothing abnormal was noted in relation to systems. The chest roentgenogram was normal and all biochemical and hematological investiga- tions revealed no abnormality. Clinically, the lump was diagnosed as an enlarged lymph node. It was aspirated using a 22-gauge needle. The lump was surgically removed, and at operation it was found to be discrete, round, and firm. According to the operating surgeon, al- though it appeared somewhat adherent to the surrounding structures, no relationship to any nerves was identified.

Cytohistologic Findings Papanicolaou stained Schleicher and Schuell filter prepa- rations and cytospin preparations from aspirated material

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NEURILEMOMA MIMICKS ADENOMA

showed mainly fragments of cellular tumour tissue with two populations of cells. One of these comprised of cohe- sive, benign, spindle-shaped cells with a pattern of swirling and interlacing fascicles in a somewhat basophilic-type ground substance material. The nuclei were somewhat plump to rounded, with some suggestion of palisading (Figs. 1A and 1B). The chromatin was finely granular. The nucleoli were indistinct, and no mitotic figures were found. The cytoplasm was eosinophilic with indistinct borders. The second population of cells showed a some- what less cohesive effect of spindle-shaped and epithelial- like cells (Figs. 2A and 2B). No distinct Verocay bodies, siderophages, or lipid-laden macrophages were identified.

The surgical specimen consisted of a 3 x 2.5 cm firm, round tumour that was uniform on the cut surface. Hema- toxylin-eosin stained sections from the tumour and cell block (subsequently made from aspirate material) showed an identical picture. These showed a spindle cell tumour with varying cellularity, in which cells suggesting an align- ment of nuclei in parallel rows with palisading arrange- ments were noted (Fig. 3). In addition, less cellular areas were seen with spindle-shaped cells in a somewhat loose collagenous matrix (Fig. 3). No mitoses were seen. The histological appearances in the tissue and cell block were diagnostic of a neurilemoma.

On a review of Papanicolaou stained cytologic material, the cytologic appearances did reveal the composite picture with admixture of stromal and cellular elements that had given the impression Of the stromal and epi- Fig. 2. (A,B) Cytologic preparation showing the second population of

spindle-shaped and epithelial like cells (Papanicolaou stain, X 350).

Fig. 1. (A,B) Cytologic preparation of aspirate showing cohesive spin- dle-shaped cells with pattern suggestive of swirling, interlacing, and palisading (Papanicolaou stain, X 350).

Fig. 3. Histologic features of neurilemoma in cell block preparation from aspirate (Hematoxylin-eosin stain, X 450).

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GUPTA AND DOWLE

thelial-like cells, resulting in the cytologic impression of a pleomorphic adenoma. Immunocytochemical staining with anti-s- 100 protein antibodies was subsequently done on stained and destained cytologic preparations from the aspirated material, and it was found to be positive in the tumour cells. Although the positivity of anti-S-100 in- directly supported the diagnosis of a neurilemoma, it was not considered conclusively diagnostic, since anti-S- 100 may be positive in both neurilemoma and pleomorphic adenoma. We did not prepare any air-dried preparations for performing the MGG staining, and thus we are unable to comment whether this staining would have helped in making the distinction between them.

Discussion Tumours of neural sheath origin are somewhat rare. The multiplicity of nerves between the base of skull and clavi- cles makes the head and neck region a site of their predi- lection. Despite some controversies, a common origin from Schwann cells is now accepted. The majority of neurilemomas present as a palpable lump. Therefore, these are likely to be subjected to NAC and may be seen more frequently by cytopathologists. Also, since the cyto- logic features of these tumours have only been described rarely, 3-8 it is quite possible that the cytopathologist may face some difficulty in the exact interpretation of NAC features of these tumours, especially since some of these may mimick other benign tumours, for example, a pleo- morphic adenoma. This was true in the case described herein.

Although it is true that pleomorphic adenomas are seen more commonly in salivary glands and as a rule show epithelial and stromal components with spindle cells and a heavy myxoid-chondroid matrix in the background (a feature not seen in neurilemomas), in some cases the spin- dle-shaped cells may predominate. In view of this, it is quite important to emphasise that a potential pitfall in the aspiration diagnosis of a neurilemoma may occur. This was addressed in a case recently reported in the literatu- re lo and which the case described herein closely resem- bled. We also agree that the fibrillary quality of matrix, the segmented palisading of nuclei, and the absence of heavy

myxoid-chondroid matrix in the background of neurilemomas may be valuable features in preventing the misinterpretation of a cytologic diagnosis in an aspirate. In differential diagnosis, other spindle-cell tumours and epithelial tumours may require an exclusion, and these have been adequately discussed in recent studies, 6,7,10 with which we are in agreement.

In summary, it is felt that neurilemomas in the head and neck region may present a problem in cytodiagnosis and may even mimic a pleomorphic adenoma. The awareness of this potential pitfall may be quite useful in preventing a misinterpretation, since it could effect a timely decision of appropriate management.

Acknowledgment The authors gratefully acknowledge the excellent secretar- ial and typing assistance of Mrs. Sharda Lallu and Mrs. Christine Christoforou in this manuscript. The technical assistance of Mr. Robert Fauck is also acknowledged.

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