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Case History 
A 61-year-old woman submitted to our institution complaining of a mass in the left submandibular region for duration of almost a year. She had a medical history of total thyroidectomy and postoperative radioactive iodine therapy for multiple thyroid papillary carcinomas. Ultrasonography imaging demonstrated the presence of a hypoechoic solid mass measuring 22 × 13 mm located in submandibular gland. At magnetic resonance imaging, it was reported as a solid lesion with smooth borders in the left submandibular gland, approximately 21 × 16 mm in size, hyperintense on T2, and showing heterogeneous contrast enhancement after intravenous contrast material injection.
FNA was performed at radiology department under ultrasonographical guidance. Direct smears were prepared. Most of the smears were air-dried and stained with May-Grunwald-Giemsa. Rest of the smears was fixed in alcohol and they were stained with Papanicolaou and Hematoxylin-Eosin.
Aspirates were cellular, composed of clusters, large tissue fragments and few single cells. The cells were spindle shaped, with oval to fusiform nuclei, fine chromatin, and moderate amount of cytoplasm with indistinctive borders [Figure 1]a. Spindle cells were uniform in most areas, few showed mild pleomorphism [Figure 1]b. Some of these cells had marked hemosiderin pigment in the cytoplasm and occasional intranuclear inclusions were observed [Figure 2]a. In some areas, spindle cells were embedded in metachromatic non-fibrillary matrix. Few lymphocytes were seen in the background. Focal palisading of tumor cells consistent with Verocay bodies was also noted [Figure 2]b. Mitosis was absent. Diagnosis of benign peripheral nerve tumor, consistent with schwannoma was given according to cytological features.
Figure 1: Fine needle aspiration smear showing (a) spindle cells with oval-fusiform nuclei, fine chromatin in a metachromatic loose matrix (MGG, 200×). (b) In focal areas mild nuclear pleomorphism is present (MGG, 400×)
Figure 2: (a) Some cells have prominent intracytoplasmic hemosiderin pigment with occasional intranuclear inclusions (high lightened with arrows) (MGG, 400×). (b) Verocay body formed by palisading of spindle cells (Hematoxylen and Eosin stain, 100×)Patient was operated a month later. At macroscopic examination, a well-demarcated lobulated white to tan mass measuring 2 × 2 × 1.5 cm was seen. Microscopy revealed spindle-cell neoplasm with hypercellular and hypocellular areas [Figure 3]a. Tumor cells were spindled and had elongated wavy nuclei with pointed ends. There was not conspicuous pleomorphism. Focal palisading of tumor cells and few intracytoplasmic hemosiderin pigments were present. With immunohistochemical staining diffuse and strong S-100 antibody positivity was detected [Figure 3]b. Histomorphological and immunohistochemical features supported the diagnosis of schwannoma.
Figure 3: (a) Encapsulated spindle cell neoplasm having relative hypocellular areas, surrounded by salivary gland lobules (Hematoxylen and Eosin stain, 20×). (b) Positive immunostaining with S-100 antibody (20×) Discussion FNA is widely used for diagnosing salivary gland masses. Most salivary gland neoplasms are epithelial in nature; on the other hand, spindle cell lesions of salivary glands compromise 3% of all salivary gland aspirates.[1] The main diagnostic approach when evaluating a spindle lesion is to determine whether the lesion is non-neoplastic/reactive process, and if it is neoplastic, it is benign or malignant.
Schwannoma is a benign mesenchymal neoplasm, which may arise from any peripheral nerve.[2] Although head and neck region is a common site for this neoplasm, submandibular gland location is extremely rare which has been documented as case reports. Accurate diagnosis of schwannoma from resection specimens are usually unproblematic, presenting as spindle cell neoplasm with pointed end nuclei, hypocellular and hypercellular areas, and Verocay bodies. It is quite the same for cytology, when it has the characteristic appearance. However, in most instances, cytomorphological features do not full fit the diagnostic criteria, or may be confused with a variety of nonneoplastic conditions and neoplasms, and usually a diagnosis as spindle cell neoplasm/lesion is rendered.
In the present case, aspirates were cellular, having many spindle cell clusters and tissue fragments. In most areas, spindle cells were bland looking with focal mild pleomorphism. Also intranuclear pseudoinclusions, palisading of tumor cells forming Verocay bodies, intracytoplasmic hemosiderin pigment, and few lymphocytes were noted. No mitotic figures were identified. Regarding to cytological features, case was reported as schwannoma.
At salivary glands, majority of the masses are epithelial in nature and most are easily diagnosed by FNA. However, spindle cell lesions are infrequent and pose cytologic diagnostic difficulties occasionally. Besides benign and malignant neoplasms, nonneoplastic/reactive conditions should bear in mind when dealing a spindle cell lesion.
Myoepithelial cells with spindle morphology and fibromyxoid stroma within the spindle cell clusters may lead to a diagnosis of pleomorphic adenoma at FNAs.[3],[4] Spindle cells forming bundles or fascicle and fibrous stroma in nodular fasciitis may have similar appearance with schwannoma.[5] Myoepitheliomas having pure spindle cell morphology may also be confused with schwannoma.[6] Another spindle cell neoplasm, solitary fibrous tumor, may pose diagnostic challenge with schwannoma; but wispy, collagenous material and capillaries accompanying to spindle neoplastic cells are clues for solitary fibrous tumor.[7] The macrophages and lymphocytes that were noted among spindle cell clusters could be encountered for features of a nonneoplastic reactive process as in granulation tissue.[1] In the present case among spindle cell clusters and tissue fragments, intranuclear inclusions and characteristic Verocay bodies led to the diagnosis of schwannoma.
In conclusion, when evaluating a spindle cell neoplasm at salivary glands, however rare, schwannoma should be kept in mind and be in the differential diagnosis. Careful examination of the cytological features is essential for accurate diagnosis and preventing unnecessary surgery.
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References 
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CheckDOI: 10.4103/joc.joc_191_21
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