Crystalloids in salivary gland lesions.

A 64-year-old male presented with swelling in front of the left ear since 2 years. There was no associated pain, fever, weight loss or hearing loss. The swelling did not increase in size during salivation. Clinical examination revealed a firm swelling of size 1 cm × 1 cm in the left parotid region.

Ultrasonography revealed a homogenously hypoechoic lesion with posterior acoustic enhancement in the parotid gland suggesting a benign lesion. Fine needle aspiration (FNA) cytology of the parotid swelling was performed from which 0.1 mL of clear fluid was aspirated. The FNA smears showed the presence of numerous crystalloids that were rectangular and rhomboid in shape with long parallel sides, some with pointed ends. They appeared bright orange on Papanicolaou stain [Figure 1] and deep blue on May-Grünwald-Giemsa stain [Figure 2]. No ductal or acinar elements were seen. In the presence of these crystals, possibility of a benign lesion was considered, and histopathological examination was suggested for confirmation following that superficial parotidectomy was done.

Figure 1

Fine needle aspiration smears showing bright orange rectangular and rhomboid crystalloids (Pap, ×400)

Figure 2

Fine needle aspiration smear showing deep blue rectangular crystalloids with pointed ends (MGG, ×400)

The parotidectomy specimen measured 5 cm × 4 cm. Cut section showed an ill-defined gray brown area measuring 1 cm × 1 cm. Rest of the parotid appeared normal. Histopathological examination of salivary gland tissue showed ducts of varying degrees of dilatation, some showing oncocytic lining epithelium. One of the dilated ducts was ruptured with wall and lumen containing collection of foam cells, giant cells and numerous pink crystalloids of similar morphology as in cytology [Figure 3]. Surrounding salivary gland showed focal atrophy of acini, dense mixed inflammatory cell infiltration, fibrosis and fatty infiltration. Based on the above findings, a diagnosis of chronic sialadenitis with crystalloids was made.

Figure 3

Salivary gland tissue showing dense inflammatory cell infiltration and scattered pink crystalloids (H and E, ×400)

Discussion

Crystalloids are encountered in a variety of salivary gland lesions. Though uncommon, they have been documented in both benign and malignant lesions. Several types of crystalline structures such as amylase, tyrosine, collagenous, oxalate and intraluminal crystalloids have been described in neoplastic and nonneoplastic salivary gland lesions.[1] It is important to recognize the type of crystalloid as they may help in differentiating benign and malignant lesions.

Tyrosine rich crystalloids have sun-burst or petal shaped morphology with blunt ends. They occur mainly in pleomorphic adenomas and rarely in malignant salivary gland neoplasms. Collagenous crystalloids are seen as radially arranged needle-shaped fibers of collagen. They have been identified in pleomorphic adenomas and myoepitheliomas. Intraluminal crystalloids composed of dense amorphous eosinophilic material are described in malignant salivary gland tumors. Alpha-amylase (α-amylase)crystalloids are nonbirefringent, rhomboid-shaped structures with pointed ends that stain bright orange with Pap stains, deep blue by May-Grόnwald-Giemsa stains and pink by hematoxylin-eosin stains. They range in size from 5 μm to 500 μm. α-amylase crystalloids have so far been reported only in benign lesions including chronic sialadenitis, unilocular cysts, and lymphoepithelial cysts.[2] They should be differentiated from all the other crystalloids as their presence most likely favors a benign lesion.

Crystalloids seen in our case morphologically resemble α-amylase described in the literature. The α-amylase crystalloids were first seen by Takeda and Ishikawa in a salivary duct cyst in 1983.[3] They concluded that these crystalloids resulted from supersaturation of saliva and represent crystallized amylase. In 1993, Jayaram et al.[4] first reported the presence of such crystalloids in FNA cytology (FNAC) of a benign cystic lesion of the parotid glands. In addition to morphology, Boutonnat et al.[5] used transmission electron microscopy, mass spectrometry and measurement of amylase activity to characterize the nature of amylase crystalloids.

In summary, a cytopathologist should include sialadenitis in the differential diagnosis of salivary gland enlargement while examining aspirates from salivary gland lesions. Also, identification of different types of crystalloids will help in deciding the nature of salivary gland lesions. Thus, making an accurate diagnosis of this lesion from FNAC samples of salivary gland will be useful to clinicians in adopting conservative management.