2Department of Oral and Maxillofacial
adenoma of the parotid
1Division of Clinical Pathology, University
Surgery, St Luc University Hospital,
University Hospital, Brussels, Belgium
any salivary gland, but is most frequently
found in the parotid gland. Chondroid metapla-
sia is a frequent finding in pleomorphic adeno-
ma. 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 schwanno-
Jean-Christophe Tille1, Hervé Reychler2,
Marc Hamoir3, Sandra Schmitz3,
Hospital of Geneva, Switzerland;
3Department of Head and Neck Surgery;
4Department of Pathology, St Luc
Pleomorphic adenoma is the most common
benign salivary gland tumour. It can occur in
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 sublin-
gual and the floor of the mouth, where most of
them are malignant.
Salivary gland tumors account for about 3%
of all head and neck neoplasia. The parotid
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 exten-
A 47-year-old woman was referred to us for a
pain localized in the right retromandibular
sion, 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
showed an intra-glandular, well delimited,
white and firm, homogeneous nodule of 3.5cm
of size. Histopathologically the tumor was com-
pletely circumscribed by a thin fibrous capsule.
The major part of the tumor consisted of spin-
dle 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 demon-
strated 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 salivary gland tumour, of which approx-
imately 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.2It is usually a solitary slow grow-
ing painless mass.
Pleomorphic adenomas are known for their
morphologic and architectural variability. They
share common features of epithelial, myoep-
ithelial and mesenchymal components. The
proportion of each of these elements can vary
widely.1The 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
Squamous cell metaplasia in pleomorphic
adenoma is an uncommon and most often acci-
dental finding.3-6Squamous cell metaplasia has
been reported as a potential pitfall in fine-needle
aspiration cytology (FNAC) of pleomorphic ade-
noma, 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.7In a
series of 10 benign parotid lesions following
Benign mixed tumour, also referred to as
pleomorphic adenoma, is the most common
FNAC, they found 8 cases of squamous cell meta-
plasia. 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-meta-
plasia. Experimental data support this hypothe-
sis, squamous metaplasia can be induced in rat
salivary glands by arterial ligation.8FNAC can
also induce necrosis and then ischemia, which
may support this last explanation.
Osseous metaplasia can be found in all sali-
vary gland locations such as the parotid, sub-
mandibular and minor salivary glands. In some
cases an important chondroid matrix was pres-
ent with the formation of enchondral ossifica-
tion at the borders.9Others described the for-
mation of osteoid indicating a possible direct
[page 126][Rare Tumors 2011; 3:e40]
Rare Tumors 2011; volume 3:e40
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.
Key words: salivary gland, parotid, metaplasia,
pleomorphic adenoma, schwannoma-like.
Conflict of interest: the authors report no con-
flicts of interest.
Received for publication: 20 April 2011
Accepted for publication: 23 August 2011
This work is licensed under a Creative Commons
Attribution NonCommercial 3.0 License (CC BY-
©Copyright J.C. Tille et al., 2011
Licensee PAGEPress, Italy
Rare Tumors 2011; 3:e40
Figure 1. Magnetic resonance imaging of
the patient with a radio opac lesion in the
right parotid gland.
[Rare Tumors 2011; 3:e40][page 127]
differentiation from myoepithelial cells10,11
Osseous metaplasia can also be found in carci-
noma ex pleomorphic adenoma12,13and mixed
tumour of the skin.14,15
To our knowledge only five cases of schwan-
noma-like pleomorphic adenoma were report-
ed in the English literature.16-18Previous 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 classi-
cal pleomorphic adenoma.
Spindle cell tumours are rare in the salivary
glands, representing from 1.9% to 5% of
parotid neoplasms.1,19,20Differential 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
Immunohistochemistry (IHC) may solve
this dilemma. Leiomyomas are negative for
cytokeratin positive for smooth muscle mark-
ers including alpha-smooth muscle actin,
desmin and caldesmon, whereas benign neu-
rogenic tumours, also negative for cytokera-
tine, 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 myoepithe-
lial origin.17The pathogenesis of this phenom-
enon could be a result of plasticity of myoep-
Fine needle aspiration cytology is an impor-
tant 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 chal-
lenging. 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 dif-
ferentiate these entities.
17. Washington, DC: AFIP; 1995. pp. 7-23.
2. Mendenhall WM,
Werning JW, et al. Salivary gland pleomor-
phic adenoma. Am J Clin Oncol 2008;
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 diagnosis.
Otolaryngol Head Neck Surg 2005;133:987-
4. Jayaram G, Pathmanathan R, Khanijow V.
Cystic lesion of the parotid gland with
squamous metaplasia mistaken for squa-
mous cell carcinoma. A case report. Acta
5. Lam KY, Ng IO, Chan GS. Palatal pleomor-
phic adenoma with florid squamous meta-
plasia: a potential diagnostic pitfall. J Oral
Pathol Med 1998;27:407-10.
6. Su CC, Chou CW, Yiu CY. Neck mass with
marked squamous metaplasia: a diagnos-
tic pitfall in aspiration cytology. J Oral
Pathol Med 2008;37:56-8.
7. Li S, Baloch ZW, Tomaszewski JE, LiVolsi
VA. Worrisome histologic alterations fol-
lowing fine-needle aspiration of benign
parotid lesions. Arch Pathol Lab Med
8. Dardick I, Jeans MT, Sinnott NM, et al.
Salivary gland components involved in the
formation of squamous metaplasia. Am J
9. Kato H, Kanematsu M, Ando K, et al.,
Ossifying pleomorphic adenoma of the
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Australas Radiol 2007;51 Suppl:B173-175.
10. Lee KC, Chan JK, Chong YW. Ossifying
pleomorphic adenoma of the maxillary
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11. Nakano K, Watanabe T, Shimizu T,
Kawakami T. Immunohistochemical char-
1. Ellis GL, Auclair PL, Tumors of the Salivary
Glands. In: Atlas of Tumor Pathology. Fasc.
Figure 2. (A) Low magnification of schwan-
noma-like pleomorphic adenoma with
both components (hematoxylin-eosin,
magnification 100x); (B) Pathologic fea-
tures of the schwannoma-like pleomorphic
adenoma with palisading spindle-shaped
cells (hematoxylin-eosin, magnification
Figure 3. Immunohistochemical staining
with (A) p63 and (B) CD10 (magnification
for A: 400x, and B: 200x).
Table 1. Schwannoma-like features in pleomorphic addenoma. Review of the literature.
Takeda et al.199918
Kajor et al.200616
Merino et al.197717
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ma: CT findings. J Comput Assist Tomogr
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Shimizu H.Immunohistochemical study of
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