Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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October 19, 2017
Sialoblastoma
- Background:
- Pediatric head and neck tumors are rare, representing about 2–3% of all head and neck tumors.
- Salivary gland tumors in children are rare. About 50% of parotid tumors in this group of children are malignant.
- Sialoblastoma was previously known as “embryoma” because of its predominance in neonates and young children.
- Although sialoblastoma was previously thought to be benign, in 2005 the World Health Organization reclassified it as a malignant epithelial salivary gland neoplasm. It has an estimated incidence of 0.8 per million children and represents <5% of all salivary gland cancers.
- Clinical Presentation:
- Sialoblastoma is an extremely rare congenital salivary gland tumor of epithelial origin, usually localized in the parotid gland.
- It is unique to children and has been reported only in newborns and neonates.
- It has an aggressive behavior at the moment of presentation.
- Sialoblastoma is known to be locally infiltrative and may metastasize to the lymph nodes or lungs if left untreated.
- Signs and symptoms may include but are not limited to a parotid region mass, difficulty in swallowing, facial paralysis, and in some cases, even skin infiltration.
- Key Diagnostic Features:
- There seem to be no pathognomonic images. CT usually shows a large, soft-tissue mass isodense to the masticatory space muscles. MRI reveals a low–intermediate signal intensity mass on T1WI and slightly higher intermediate signal intensity on T2WI.
- About 25% of sialoblastomas show aggressive features such as local infiltration, but distant metastases are rare.
- Determining the epicenter of the lesion in the parotid space and discarding a bone origin, together with the patient’s age, may help with including this tumor in the differential diagnosis.
- Differential Diagnoses:
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Pleomorphic adenoma is the most common benign tumor in the superficial parotid lobe and does not destroy adjacent bone. In pediatric patients it has a median age of 15 years (range of 1–20 years).
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Mucoepidermoid carcinoma is the most common malignant epithelial tumor and is typically found in middle age (35–65 years). Prior radiation therapy has been suggested as a risk factor. It is the most common primary malignant salivary gland neoplasm described in children.
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Adenoid cystic carcinoma is predominantly an adult tumor, with a peak incidence in the fourth to sixth decade of life and a female predominance. It occurs mainly in the minor salivary glands and particularly in the oral cavity (palate).
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Extraskeletal Ewing sarcoma predominantly affects young adolescents and adults between 10 and 30 years of age. Although the head and neck region is an uncommon location, Ewing sarcomas involving the nose, nasopharynx, parotid gland, and cervical soft tissues have been reported.
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Liposarcoma is one of the most common types of soft-tissue sarcoma and occurs most frequently in the fifth and sixth decades of life. The imaging appearance of liposarcomas varies depending on the histologic subtype and the proportion of nonlipomatous elements. Less than 50% of malignant tumors contain macroscopic lipid content on CT.
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Kaposiform hemangioendothelioma is a locally aggressive vascular tumor of infancy. Foci of signal dephasing representing blood products may be evident on gradient-echo MRI. Most of these tumors are clinically apparent within the first year of life, and roughly half of them are present at birth. The most relevant associated clinical condition is consumptive coagulopathy (Kasabach-Merritt syndrome), which occurs in more than 50% of patients.
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Angiosarcoma is an aggressive vascular neoplasm with a high local recurrence rate and distant metastasis at the time of presentation. Soft-tissue angiosarcomas may occur at any age but are more common in older patients, with a peak incidence in the seventh decade of life.
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- Treatment:
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Treatment options include surgery, but achieving negative margins is technically challenging.
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Radiotherapy may be considered if lesions are not completely resectable, but the adverse effects of radiation therapy may be significant in the growing facial structures.
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Chemotherapy may be an option when the tumor is not completely resectable or in cases of persistent or recurrent tumor.
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