Ectopic Hamartomatous Thymoma

Abstract

This report describes the clinicopathologic and immunohistochemical findings in 21 cases of a highly distinctive tumor with a strong predilection for the lower neck region of adult males. Our study group consisted of 20 males and one female. The patients were 28 to 79 years old (mean age, 47 years; median age, 40 years), and they presented with solitary, lobular or multilobular masses ranging in size from 2.0 to 19.0 cm in greatest dimension (mean size, 5.1 cm; median, 4 cm). The tumors principally involved the lower neck region, usually in close proximity to the sternoclavicular joint. The preoperative duration of the lesions ranged from 2 months to 30 years. Histologically, the tumors were typically well marginated and composed of plump spindled cells, delicate spindled cells, mature adipose tissue, and epithelial cells, including both squamous and glandular elements. Epithelial-lined cysts were a focal finding in most cases and measured up to 2 cm in greatest dimension. Mitotic counts for the tumors ranged from 0 to 7 mitotic figures per 50 high power fields (mean mitotic count, 1.1 mitotic figures per 50 HPFs). Our immunohistochemical analysis revealed a complex immunophenotype with a diverse keratin profile. The plump spindled cells had a myoepithelial phenotype, as evidenced by the coexpression of keratins (5, 5/6, and 14), alpha-smooth muscle actin, CD10, and to a lesser extent, calponin. No compelling evidence for thymic differentiation was observed. The patients were initially managed by biopsy or partial resection (n = 4), simple local excision (n = 16), or an unspecified procedure (n = 1). Clinical follow-up of > or =3 years was available for 10 patients (48%). Two patients had recurrent disease, but there were no metastases or tumor-related deaths. A derivation from sequestered branchial epithelium is likely, but evidence for a thymic component is tenuous, at best. Our data support reclassification of this distinctive process as a branchial anlage mixed tumor. The differential diagnosis includes conventional mixed tumors of skin adnexal or salivary gland origin, synovial sarcoma, a peripheral nerve sheath tumor variant, and cystic teratoma.

Immunohistochemistry for Diagnosis of Metastatic Carcinomas of Unknown Primary Site

“…Cysts lined by a squamous epithelium, small glands and fat also occur in variable amounts. Both the spindled and epithelial regions of the tumour express cytokeratins (AE1/AE3, CK5/6, CK14) and smooth muscle actin but neither Desmin nor S100 protein, while the fibroblast-like spindle cells are positive for CD34 [ 95 ].…”

Ectopic hamartomatous thymoma (biphenotypic branchioma)

“…Ectopic hamartoma thymoma, characterized by a mixture of spindle cells, epithelial elements, and mature adipose components, is a very rare soft tissue tumor of the lower neck. [ 3 , 4 ] Our case presented in this paper has the typital clinical and pathological features of ectopic hamartomatous thymoma. Around 80 pathologically verified cases of EHT have been reported so far, we have made a summary and analysis above them (Table 2 ).…”

“…EHT is known to be a slow-growing tumor or mass. There was neither recurrence nor metastasis during follow-up of 46 cases, except for 2 patients who had recurrence because of incomplete local excision as reported by Fetsch et al [ 3 ] Local surgical resection is the first choice of treatment because of its good clinical outcome. [ 3 , 7 ]…”

Metaplastic Thymoma: Report of 4 Cases

“…It is noteworthy that EHT is a benign tumor of the lower neck showing an admixture of epithelial islands with spindle and adipose cells. This tumor is not deep-seated, and cytokeratin is positive in both epithelial and spindle cell component with at least focal glandular differentiation 10-12. In contrast to EHT, MT exhibits alternating areas of epithelial and spindle cell component, which is highlighted by immunostaining for cytokeratin and vimentin, respectively.…”