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Schwannoma-like pleomorphic adenoma of the parotid.
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PMID:  22355495     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Pleomorphic adenoma is the most common benign salivary gland tumour. It can occur in any salivary gland, but is most frequently found in the parotid gland. Chondroid metaplasia is a frequent finding in pleomorphic adenoma. Other forms of metaplasia have been described, but are encountered less frequently. We report a rare case of unusual pleomorphic adenoma of the parotid gland with schwannoma-like feature.
Jean-Christophe Tille; Hervé Reychler; Marc Hamoir; Sandra Schmitz; Birgit Weynand
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Publication Detail:
Type:  Journal Article     Date:  2011-09-16
Journal Detail:
Title:  Rare tumors     Volume:  3     ISSN:  2036-3613     ISO Abbreviation:  Rare Tumors     Publication Date:  2011 Oct 
Date Detail:
Created Date:  2012-02-22     Completed Date:  2012-10-02     Revised Date:  2013-05-29    
Medline Journal Info:
Nlm Unique ID:  101526926     Medline TA:  Rare Tumors     Country:  Italy    
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Languages:  eng     Pagination:  e40     Citation Subset:  -    
Division of Clinical Pathology, University Hospital of Geneva, Switzerland;
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Journal ID (nlm-ta): Rare Tumors
Journal ID (pmc): RT
Journal ID (publisher-id): RT
ISSN: 2036-3605
ISSN: 2036-3613
Publisher: PAGEPress Publications, Pavia, Italy
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©Copyright J.C. Tille et al., 2011
Received Day: 20 Month: 4 Year: 2011
Accepted Day: 23 Month: 8 Year: 2011
Electronic publication date: Day: 16 Month: 9 Year: 2011
collection publication date: Day: 21 Month: 10 Year: 2011
Volume: 3 Issue: 4
E-location ID: e40
ID: 3282445
PubMed Id: 22355495
Publisher Id: rt.2011.e40
DOI: 10.4081/rt.2011.e40

Schwannoma-like pleomorphic adenoma of the parotid
Jean-Christophe Tille1
Hervé Reychler2
Marc Hamoir3
Sandra Schmitz3
Birgit Weynand4
1Division of Clinical Pathology, University Hospital of Geneva, Switzerland;
2Department of Oral and Maxillofacial Surgery, St Luc University Hospital, Brussels, Belgium;
3Department of Head and Neck Surgery;
4Department of Pathology, St Luc University Hospital, Brussels, Belgium
Correspondence: Correspondence: Jean-Christophe Tille, University Hospital of Geneva, Department of Genetics and Laboratory Medecine, Division of Clinical Pathology, Rue Gabrielle-Perret-Gentil 2, 1211 Geneva 4, Switzerland. Tel. +41.22.372.49.19 - Fax: +41.22.372.49 20. E-mail:
[conflict] Conflict of interest: the authors report no conflicts of interest.


Salivary gland tumors account for about 3% of all head and neck neoplasia. The parotid gland is the main site for these tumors and about 95% of them are of epithelial origin.1 Benign tumors represent 54% to 79% and 21% to 46% are malignant. The proportion of benign versus malignant tumor varies greatly by site. In the major salivary glands, such as the parotid and the submandibular gland, the majority of the tumors are benign contrary to the minor salivary glands, such as the sublingual and the floor of the mouth, where most of them are malignant.

Case Report

A 47-year-old woman was referred to us for a pain localized in the right retromandibular area, since about two months. Careful head and neck palpation revealed only a slight swelling in the right retromandibular region, without any well delineated palpable tumor. Head and neck MRI revealed a well defined tumor of 3.2 cm of size in the deep lobe of the right parotid gland with parapharyngeal extension, consistent with a pleomorphic adenoma (Figure 1). A right total parotidectomy with identification and preservation of the facial nerve was performed to remove the tumor appropriately. Macroscopic examination showed an intra-glandular, well delimited, white and firm, homogeneous nodule of 3.5cm of size. Histopathologically the tumor was completely circumscribed by a thin fibrous capsule. The major part of the tumor consisted of spindle cells with nuclear palisading resembling Verocay bodies (Figure 2B). At the periphery, some foci were composed of myxoid stroma with epithelial and myoepithelial-lined tubules (Figure 2A). Immunohistochemistry demonstrated the expression of p63 (Figure 3A) and CD10 (Figure 3B) in both tumour components and cytokeratin was positive in epithelial and myoepithelial cells. Histopathology diagnosis was a schwannoma-like pleomorphic adenoma of the parotid gland.


Benign mixed tumour, also referred to as pleomorphic adenoma, is the most common benign salivary gland tumour, of which approximately 80% occur in the parotid gland, 10% in the submandibular glands and 10% in the minor salivary gland of the oral cavity. This tumour is most often observed in 30 to 60 years old patients and is more frequent in women than in men.2 It is usually a solitary slow growing painless mass.

Pleomorphic adenomas are known for their morphologic and architectural variability. They share common features of epithelial, myoepithelial and mesenchymal components. The proportion of each of these elements can vary widely.1 The stromal component of these tumours is most often predominantly myxoid with focal chondroid or fibrous aspects. Modified myoepithelial cells are thought to play an important role in the histopathological changes of the stroma. Sometimes squamous or osseous metaplasia is found in pleomorphic adenoma but is encountered less frequently. On a retrospective study on 83 pleiomorphic adenomas over a period of five years, we found an overall prevalence of 5% of metaplasia (unpublished data).

Squamous cell metaplasia in pleomorphic adenoma is an uncommon and most often accidental finding.36 Squamous cell metaplasia has been reported as a potential pitfall in fine-needle aspiration cytology (FNAC) of pleomorphic adenoma, which can be confused with a squamous cell or mucoepidermoid carcinoma. Different hypotheses have been advanced for its etiopathology. Firstly, it may be a repair process following FNAC, as reported by Li et al.7 In a series of 10 benign parotid lesions following FNAC, they found 8 cases of squamous cell metaplasia. In our case, we did not have any proof of a previous FNAC. A second hypothesis could be intra-lesional ischemia as it can be found in chronic sialadenitis or necrotizing sialo-metaplasia. Experimental data support this hypothesis, squamous metaplasia can be induced in rat salivary glands by arterial ligation.8 FNAC can also induce necrosis and then ischemia, which may support this last explanation.

Osseous metaplasia can be found in all salivary gland locations such as the parotid, submandibular and minor salivary glands. In some cases an important chondroid matrix was present with the formation of enchondral ossification at the borders.9 Others described the formation of osteoid indicating a possible direct differentiation from myoepithelial cells10,11 Osseous metaplasia can also be found in carcinoma ex pleomorphic adenoma12,13 and mixed tumour of the skin.14,15

To our knowledge only five cases of schwannoma-like pleomorphic adenoma were reported in the English literature.1618 Previous cases included four women and one man, aged from 39 to 75 years (Table 1). The majority of the lesions, as ours, were located in the parotid gland with one exception in the hard palate. All cases including this one had palisading areas of spindle-shaped cells in an otherwise classical pleomorphic adenoma.

Spindle cell tumours are rare in the salivary glands, representing from 1.9% to 5% of parotid neoplasms.1,19,20 Differential diagnoses of benign spindle cell tumours in salivary glands include neurogenic tumours: schwan-noma, composed of areas with Verocay bodies and neurofibroma, as well as smooth muscle proliferations: leiomyoma.

Immunohistochemistry (IHC) may solve this dilemma. Leiomyomas are negative for cytokeratin positive for smooth muscle markers including alpha-smooth muscle actin, desmin and caldesmon, whereas benign neurogenic tumours, also negative for cytokeratine, express neurogenic marker (S100-Protein, CD57 and neurofilament).

Shwannoma-like pleomorphic adenomas are composed of modified myoepithelial cells expressing p63, CD10 and cytokeratin by IHC.16 Merino et al. demonstrated the presence of desmosomes in these spindle-shaped cells by electron microscopy confirming a myoepithelial origin.17 The pathogenesis of this phenomenon could be a result of plasticity of myoepithelial cells.

Fine needle aspiration cytology is an important diagnostic procedure used to evaluate salivary gland lesions and to help in their pre-operative management. Typically, FNAC of pleomorphic adenoma shows a combination of cohesive epithelial cells in a pale myxoid matrix. When the cellularity is abundant and no matrix is identified this diagnosis is challenging. In the presence of spindle-shaped cells immunohistochemical analysis may be used to identify the myoepithelial phenotype.

Pleomorphic adenoma with schwanoma-like feature is a rare variant that could be confused with a schwannoma or a leiomyoma, but immunohistochemical study is helpful to differentiate these entities.

1. Ellis GL,Auclair PL. Tumors of the Salivary GlandsAtlas of Tumor Pathology. Fasc. 17Washington, DCAFIPYear: 1995723
2. Mendenhall WM,Mendenhall CM,Werning JW,et al. Salivary gland pleomorphic adenomaAm J Clin OncolYear: 20083195918376235
3. Hamdan K,Maly B,Elashar R,Gross M. Mucinous and squamous metaplasia in benign tumors of the parotid gland: a potential pitfall in the diagnosisOtolaryngol Head Neck SurgYear: 2005133987816360528
4. Jayaram G,Pathmanathan R,Khanijow V. Cystic lesion of the parotid gland with squamous metaplasia mistaken for squamous cell carcinoma. A case reportActa CytolYear: 1998421468729850664
5. Lam KY,Ng IO,Chan GS. Palatal pleomorphic adenoma with florid squamous metaplasia: a potential diagnostic pitfallJ Oral Pathol MedYear: 199827407109736432
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7. Li S,Baloch ZW,Tomaszewski JE,LiVolsi VA. Worrisome histologic alterations following fine-needle aspiration of benign parotid lesionsArch Pathol Lab MedYear: 2000124879110629137
8. Dardick I,Jeans MT,Sinnott NM,et al. Salivary gland components involved in the formation of squamous metaplasiaAm J PatholYear: 198511933432580442
9. Kato H,Kanematsu M,Ando K,et al. Ossifying pleomorphic adenoma of the parotid gland: a case report and reviewAustralas RadiolYear: 200751SupplB17317517991056
10. Lee KC,Chan JK,Chong YW. Ossifying pleomorphic adenoma of the maxillary antrumJ Laryngol OtolYear: 19921065021311743
11. Nakano K,Watanabe T,Shimizu T,Kawakami T. Immunohistochemical characteristics of bone forming cells in pleomorphic adenomaInt J Med SciYear: 20074264618026564
12. Parikh HK,Parikh DM. Malignant mixed tumor of the salivary gland with bone metastasis: a case report and literature reviewIndian J CancerYear: 19912817151664816
13. Spencer J,Mason A,Denton K. Ossifying parotid carcinoma ex pleomorphic adenoma: CT findingsJ Comput Assist TomogrYear: 19911551681851189
14. Awasthi R,Harmse D,Courtney D,Lyons CB. Benign mixed tumour of the skin with extensive ossification and marrow formation: a case reportJ Clin PatholYear: 20045713293015563678
15. Shimizu S,Han-Yaku H,Fukushima S,Shimizu H. Immunohistochemical study of mixed tumor of the skin with marked ossificationDermatologyYear: 199619325578944353
16. Kajor M,Gierek T,Markowski J,Pajak J. Schwannomalike mixed tumor of the parotid gland: a case reportActa CytolYear: 2006505293017017438
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[Figure ID: F1]
Figure 1 

Magnetic resonance imaging of the patient with a radio opac lesion in the right parotid gland.

[Figure ID: F2]
Figure 2 

(A) Low magnification of schwannoma-like pleomorphic adenoma with both components (hematoxylin-eosin, magnification 100×); (B) Pathologic features of the schwannoma-like pleomorphic adenoma with palisading spindle-shaped cells (hematoxylin-eosin, magnification 200×).

[Figure ID: F3]
Figure 3 

Immunohistochemical staining with (A) p63 and (B) CD10 (magnification for A: 400×, and B: 200×).

[TableWrap ID: T1] Table 1  Schwannoma-like features in pleomorphic addenoma. Review of the literature.
Age, sex Localisation
Takeda et al. 199918 62-year-old man Parotid
48-year-old woman Hard palate
Kajor et al. 200616 75-year-old woman Parotid
Merino et al. 197717 74-years-old woman Parotid
39-years-old woman Parotid
Present case 47-years-old woman Parotid

Article Categories:
  • Case Report

Keywords: Key words: salivary gland, parotid, metaplasia, pleomorphic adenoma, schwannoma-like..

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