Metastatic spindle cell neoplasms most likely represent sarcomatoid carcinomas, melanomas and sarcomas, especially rhabdomyosarcomas. Pankeratin, MART-1, HMB-45, S-100 protein, desmin, smooth muscle ac-tin and myogenin are some immunostains that help to distinguish these neoplasms [29]. Primary spindle cell lesions arising in lymph nodes, such as Kaposi's sarcoma, presumed tumours of the reticulum cell lineage and benign intranodal myofibroblastomas, must be distinguished from metastatic spindle neoplasms [2, 56].

Undifferentiated malignant neoplasms in cervical lymph nodes need to be investigated with immunohis-tochemical studies. CK-positive malignancies with the morphology of the nasopharyngeal type of carcinomas (NPC) are usually located in the posterior neck, whereas metastasis from undifferentiated sinonasal carcinomas (SNUC) are present in the upper and mid-cervical regions. If the metastases are located in the lower neck, the lung is the most likely source. If the carcinomas in addition exhibited neuroendocrine differentiation, Merkel cell carcinoma or small cell neuroendocrine carcinoma, from either the lung or the larynx, is the best diagnosis. Merkel cell carcinomas are CK 20-positive [19] and pulmonary small cell carcinomas are CK 20-negative and TTF-1 positive in 83-100% of cases [83]. Benign nevus cells have been found in the capsules of submandibular lymph nodes. This rare finding should not lead to an erroneous diagnosis of malignancy [54].

Paccioni et al. evaluated 25 cases of occult metastasis to cervical lymph nodes for the presence of Epstein-Barr virus (EBV) by in situ hybridisation following fine-needle aspiration biopsies of the neck mass and correlated the findings with the histologic types of the surgical specimens (after locating the primary site of origin). These authors reported that EBV was expressed in 7 metastases, ultimately proving their origin from the nasopharynx, while the remaining 18 cases (not of Waldey-er's ring origin) were negative for EBV [84]. The authors indicated that detection of EBV in cervical metastases may assist in the localisation of the occult primary to Waldeyer's ring. SNUC do not express EBV [84].

The pattern of CK expression is significantly different in SNUC and NPC, which could be of diagnostic aid. Franchi et al. demonstrated that SNUC express CK 8 in 100% of cases and CK 19 and CK 7 in 50%, and are negative for CK 5/6, while NPC express CK 5/6 and CK 13 in 90% of cases and are negative for CK 7 [40].

Metastases from melanoma, rhabdomyosarcoma, and rarely from olfactory neuroblastoma should be considered with the CK-negative undifferentiated neoplasms and proper immunohistochemical markers investigated (Fig. 9.15). In CK-negative tumours, the possibility of malignant lymphoma should be considered and CD 20, CD 3 and antibodies for leukocyte common antigen should be measured [29].

Fig. 9.15. Metastatic spindle cell melanoma in a cervical lymph node

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