Sialometaplasia, squamous metaplasia of salivary gland lobules, is a benign condition occasionally presenting with lesions clinically simulating malignancy. “Necrotising sialometaplasia”, recognised by lobular infarction, necrosis, and simultaneous squamous metaplasia of ducts and acini is a well known condition. There are only a few reports of the “proliferative type of sialometaplasia”, which is recognised by a more mature morphology of larger and more irregular metaplastic nests, lacking necrosis. This report describes a unique case of “proliferative sialometaplasia of multiple intraparotid lymph nodes” occurring in a 55 year old woman, presenting with multiple parotid lumps. This interesting case points to the importance of intraparotid lymph nodes as sites for multiple lesions of the parotid region.
- LN, lymph node
- PS, proliferative sialometaplasia
- SM, squamous metaplasia
- intranodal inclusions
- intraparotid lymph nodes
Statistics from Altmetric.com
Sialometaplasia, squamous metaplasia (SM) of salivary gland lobules, is a benign condition occasionally presenting with lesions mimicking malignancy. Since the description of the necrotising type,1 many cases have been published. The proliferative form has only been reported in a few cases in intraparotid lymph nodes (LNs).2,3 This type of sialometaplasia is recognised by solid squamous metaplastic nests involving ductal structures and lacking atypia and necrosis.2
A 55 year old woman presented with left infra-auricular multiple lumps, of two years duration. She had undergone stapedectomy of the right ear five years previously.
The patient had a 1.5 × 1.5 cm, non-tender, semimobile mass in the left preauricular region, and a similar mass in the tail of the left parotid gland. The functions of the facial nerve were bilaterally normal and the examination of the other head and neck sites including the other salivary glands was unremarkable. She had no complaints of xerostomia. Sonography revealed hypoechoic parotid nodules. The lesions were hyperdense with contrast enhancement on computed tomography scans. Magnetic resonance imaging demonstrated two spherical discrete masses. Lesions were hypointense on the T1 images and isointense on the T2 images with contrast enhancement (fig 1). The radiological conclusion was consistent with a benign tumour, in particularly pleomorphic adenoma, and the clinical diagnosis was that of pleomorphic adenoma and associated lympadenomegaly of intraparotid LNs. The routine laboratory examinations were not remarkable: white blood cell count, 8.1 ×109/litre; haemoglobin, 135 g/litre; haematocrit, 39.3%; erythrocyte sedimentation rate, 21 mm/hour; antinuclear antibodies, antineutrophil cytoplasmic antibodies, human immunodeficiency virus were negative.
Left superficial parotidectomy with preservation of the facial nerve was performed.
Superficial parotidectomy revealed two encapsulated, 1.5 cm, grey/white nodules located at the poles. Histology showed that they were both LNs and six additional LNs were also identified. Five LNs revealed ductal salivary gland inclusions, almost totally replaced by SM, but retaining the lobular architecture of ductal inclusions (figs 2, 3). Ductal inclusions were also identified in another lymph node. The parotid gland showed atrophic changes.
The metaplastic squamous epithelium was keratin positive and mucicarmen negative. Smooth muscle actin and S-100 was positive at the periphery of the metaplastic lobules (fig 4). The diagnosis was that of “proliferative sialometaplasia (PS)” involving salivary gland inclusions of multiple intraparotid LNs.
The patient is well 12 months after surgery.
Lymphoid and epithelial lesions may arise from intraparotid LNs, which originate from the inclusions of salivary ducts and acini.2–7 The frequency of these lesions increases dramatically when cystadenoma lymphomatosum cases, which are thought to arise from intranodal ductal inclusions, are considered.8
Multiple lumps at this region are frequently related to lesions originating from LNs, and the leading lesion is again cystadenoma lymphomatosum.9 In our present case, histopathological examination revealed extensive SM of the intranodal inclusions, with a preserved lobular architecture involving five intraparotid LNs. Among the previous reports we noticed cases comparable to this one. Goldman and Klein2 described PS of an intraparotid lymph node. Ryan et al described two patients with AIDS who presented with lumps at the parotid region, with lymphadenitis and SM of the salivary gland ductal inclusions.3 As in our present case, those cases did not fulfill the established criteria for the diagnosis of necrotising sialometaplasia1 described by Abrams et al,1 because we could not consistently demonstrate infarction. Anneroth and Hansen10 suggested five stages in the course of necrotising sialometaplasia, namely: infarction, sequestration, ulceration, reparation, and healing. The lesions in our patient might represent the reparation and healing stages of necrotising sialometaplasia, but without evidence of necrosis the case falls into the category of proliferative SM.
Take home messages
We report a unique case of proliferative sialometaplasia of multiple intraparotid lymph nodes occurring in a 55 year old woman, presenting with multiple parotid lumps
This interesting case points to the importance of intraparotid lymph nodes as sites for multiple lesions of the parotid region
“We feel that this unique case is important because, to the best of our knowledge, this is the first case of proliferative sialometaplasia involving multiple intraparotid lymph nodes”
The differential diagnosis of proliferative SM also includes metastatic squamous cell carcinoma and mucoepidermoid carcinoma.2,10,11 In our present case, no cellular atypia or mitotic activity was encountered, thus excluding carcinoma. The coexpression of cytokeratin, S-100, and actin was consistent with a lesion related to myoepithelial cells. The lack of chondromyxoid stroma and the presence of multiple intranodal lesions aided in the exclusion of squamous metaplasia prominent pleomorphic adenoma.2 The patient’s clinical features were inconsistent with the established criteria12 of Sjögren’s syndrome and the involvement of intraparotid lymph nodes has not been described for this disease.
We feel that this unique case is important because, to the best of our knowledge, this is the first case of PS involving multiple intraparotid LNs. PS should be included in the differential diagnosis of multiple lumps of the parotid region.