Cytological Clues to the Diagnosis of Solid Variant of Papillary Thyroid Carcinoma

Sir,

The solid variant of papillary thyroid carcinoma (PTC) accounts for 3% of all cases of PTC. It constituted a disproportionately higher percentage of PTC diagnosed in children in the first decade after the Chernobyl tragedy.[1,2]

A 14-year-old girl presented with thyroid swelling measuring 2 × 2 cm to the Otorhinolaryngology Outpatient Department. She did not give any history of hyper or hypothyroidism or radiation exposure. She had noticed the swelling 6 months back. Fine-needle aspiration (FNA) cytology performed from the swelling in the left lobe of the thyroid showed thyroid follicular cells with nuclear clearing, grooving, and pseudo inclusions in a single cell and trabecular pattern. A few microfollicles and an occasional solid fragment were also noted. [Figure 1a to d] The FNA report was Bethesda category V (suspicious of PTC). The patient underwent contrast-enhanced computed tomography of the neck which showed a well-defined hypodense lesion with high vascularity and microcalcification measuring 2 × 2 cm in the left lobe suggestive of PTC with evidence of heteroechoic lymph nodes in bilateral level IV region. The patient underwent total thyroidectomy with bilateral lateral neck dissection. On gross examination, the tumor was gray-white, partly encapsulated with calcification, and measured 2.1 × 2.0 × 1.8 cm in the left lobe [Figure 2a]. On histopathology, the tumor was arranged predominantly in a trabecular and nesting pattern with nuclear clearing, grooving, and pseudoinclusions. The tumor margins were infiltrative with extrathyroidal extension. The tumor was immunonegative for chromogranin and synaptophysin. No necrosis, frequent mitosis, or nuclear atypia were seen [Figure 2b to d]. The final diagnosis given was a solid variant of papillary thyroid carcinoma. A total of seven regional lymph nodes were found to have metastasis out of 18 lymph nodes examined. The patient was referred to the oncology center for postoperative radioiodine therapy and was lost to follow-up.

Figure 1.

Fine-needle aspiration cytology of the tumor. Follicular epithelial cells are arranged in a trabecular pattern and small clusters with nuclear clearing, grooving, and pseudoinclusions (a and b, Papanicolaou stain, 400×). Single-cell pattern with nuclear features of papillary thyroid carcinoma (c, Papanicolaou stain, 400×). Occasional solid fragment of follicular epithelial cells (d, May Grunwald Giemsa, 400×)

Figure 2.

Gross appearance of the tumor-gray white with calcification (a). Histopathology of the tumor showed a tumor arranged in a follicular and trabecular pattern with nuclear clearing, grooving, and intranuclear pseudoinclusions. (hematoxylin and eosin,b-100x,c-400x). The tumor was immunonegative for chromogranin (d-400x)

A papillary variant of medullary thyroid carcinoma (MTC) has been reported. Although very rare with only a few cases been reported in literature, it is to be kept in the differential diagnosis. In these cases, the nuclear features of PTC are seen in 20 to 25% of tumor cells.[3] In MTC, the cells are often round to oval to spindle-shaped with salt and pepper chromatin and eccentric nuclei. In the absence of these features, single cell, nesting, and trabecular pattern with solid fragments and nuclear features of PTC should alert one to the possibility of a solid variant of PTC.[1] The presence of amyloid and pink intracytoplasmic granules on the May-Grunwald-Giemsa stain would help in making a diagnosis of MTC. The amyloid needs to be differentiated from the chewing gum colloid of PTC.

Higuchi et al. reported the following cytological features to be most frequent in histologically proven cases of a solid variant of PTC-grooved nuclei, intranuclear cytoplasmic inclusion, ground glass chromatin, solid clusters, and small papillary clusters and irregularly shaped nuclei.[4]

To conclude, the overlapping nuclear features of PTC and architectural features of MTC in a thyroid aspirate should alert the pathologist to the possibility of a solid variant of PTC even in absence of a history of radiation exposure. However, the solid variant of PTC is a histological diagnosis and in cytology – a diagnosis of PTC is adequate.

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