Histologic Differential Diagnosis

Figure 1. Carcinoid Tumor

Round to ovoid, central nuclei in polygonal cells with pink cytoplasm and absent mitoses characterize typical carcinoid tumors. The configuration of the blood vessels differs from the large "staghorn" type seen in glomus tumors.

Name an immunohistochemical stain that differentiates carcinoid tumors from glomus tumors.

Answer

Figure 2. Hemangiopericytoma

Spindled, rather than rounded, cells and nuclei surround irregularly-shaped, "staghorn" vessels in hemangiopericytomas. Mitoses, infiltrative margins, necrosis, and vascular or pleural invasion are more common than in glomus tumors [1].

Ultrastructurally, dense bodies and plasmalemmal plaques are absent in hemangiopericytomas.

In the lung, these tumors have been reported more frequently, and are more likely to be malignant, than glomus tumors [1].

What immunohistochemical stain separates these tumors from glomus tumors?

Answer

Figure 3. Primitive Neuroectodermal Tumor (PNET)

These malignant tumors show nuclear pleomorphism and prominent nucleoli. Mitoses are frequent. Nuclei may be rounded or spindled.

What special stain characterizes these tumors?

Answer

Reference:

1. Yousem S, Hochholzer L. Primary pulmonary hemangiopericytoma. Cancer 1987; 59:549-555. Abstract

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A positive immunohistochemical stain for chromogranin is seen in carcinoid tumors, whereas glomus tumors are negative. Carcinoid tumors are also keratin positive, whereas glomus tumors are not.

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A stain for smooth muscle specific actin (HHF35) is positive in glomus tumors and negative in hemangiopericytomas.

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O13 (CD99) positivity

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