Several features will be considered in the evaluation of the specimen:
the type of cells (such as thyrocytes, macrophages, lymphocytes)
Thyrocytes and macrophages. Fluid colloid in the background, bland thyrocytes and pigmented macrophages.
Lymphocytes and thyrocytes. A group of bland thyroid cells showing a follicular arrangement, surrounded by smaller lymphoid cells with little amount of identifiable cytoplasm. Such lymphoid cells are also inside the follicular group, suggesting chronic inflammation.
amount and type of colloid (scanty-abundant, fluid-dense)
Colloid: Fluid but relatively thick colloid with the typical cracks which are produced with air drying. These are artefacts which are useful in recognising colloid.
Colloid: A clump of thicker colloid surrounded by few bare nuclei. In the appropriate context this type of colloid may be associated with papillary carcinoma.
cellularity (scanty, moderate, marked)
Highly cellular smear showing a microbiopsy. A microbiopsy, as may be obtained with larger needles, in which 3D follicles are separated by collagenous septa; the margins of the follicles are regular. This pattern is usually seen in FNAs from nodular goitres. Please note that in air dried samples stained with MGG the centre of these microbiopsies will be too thick to assess.
Less cellular but diagnostic smear showing groups of bland thyroid cells in a microfollicular arrangement, bare nuclei of thyroid cells and fluid colloid in the background. A few macrophages are also present. This pattern is associated with benign disease.
architecture (monolayers, crowded clusters, sheets, macro/microfollicles, papillary clusters, isolated cells)
Sheets of bland thyroid cells. A monolayered sheet of bland thyroid cells. Note the regular distribution of the nuclei and cytoplasm and very fine chromatin with small nucleoli.
Sheets of bland thyroid cells. Another example of a a monolayered sheet of bland thyroid cells. Because of the size of this sheet some areas may appear more crowded but are actually simply folded. It is good practice to focus on these areas to check the regular distribution of cells along the same plane. Such large sheets are usually lining larger follicles or cysts in benign disease.
Thyroid cells in a microfollicular arrangement. Several groups of thyroid cells in a microfollicular arrangement. In follicular lesions this may be the only type of cell present.
A papillary cluster with the epithelial cells lying perpendicular to the stromal axis. The typical nuclear features of papillary carcinoma need to be present however for a diagnosis of papillary carcinoma. .
Many bare nuclei are seen dispersed together with bland thyroid cells in a follicular arrangement. Note that the chromatin pattern is the same, confirming that these nuclei have been stripped of their fragile cytoplasm during the smearing procedure. Lymphocytes are smaller, have a more granular chromatin, folded nuclear membrane and scanty but clearly identifiable, dense cytoplasm.
cytologic features (cytoplasm, nuclei)
In neoplastic lesions the specimens are usually highly cellular. Flat sheets are common in goitre and macrofollicular adenomas, but can also be present in carcinomas. Macrofollicles are usually associated with multinodular goitre and macrofollicular adenomas. A predominance of microfollicles can be suggestive of a follicular neoplasm. Papillary clusters, with cells lining a fibrovascular core, are characteristic of papillary carcinoma. Smears with a high ratio of colloid to follicular cells usually indicate a benign nodule.
cytoplasm (amount, staining)
nuclear membrane (smooth or irregular)
nuclear groovings and pseudoinclusions
Abundant cytoplasm containing granules. A group of large non cohesive cells with abundant dense, cytoplasm containing granules. The nuclei are single or multiple and pleomorphic. The differential includes Hürthle cells (oncocytic change), “squamoid" cells in papillary carcinoma or goitre and atypical cells in anaplastic carcinoma.
Nuclear pseudoinclusions and groovings. A cluster of large cells with abundant, polygonal and dense cytoplasm; the nuclei in this case show all the features of papillary carcinoma (nuclear pseudoinclusions, grooving).