Atypical parathyroid adenoma
The patient presented to her GP with a several week history of unexpected fatigue and lethargy. Upon questioning, her doctor elicited the additional symptoms of generalised joint aching and a vague abdominal discomfort, along with appetite loss and minor unintentional weight loss. Initial blood tests revealed an elevated calcium and additional testing showed a high PTH level and low phosphorous. Following sestamibi and CT imaging tests, the patient progressed to surgery and a frozen section was received in the lab.
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Macroscopic and Microscopic Findings
The specimen consists of a 1.20g, 12 mm well circumscribed tumour with peripheral fibrous capsule, composed of solid sheets of parathyroid epithelial oncocytic cells showing a vaguely organoid architecture without interspersed fat and showing a scant amount of peripheral normal appearing parathyroid gland. Tumour cells are medium in size with rounded to ovoid nuclei and a moderate amount of oncocytic cytoplasm. Thick, hyalinised fibrous stromal band traverse the lesion. There is no tumour cell necrosis or haemorrhage. There is no significant mitotic activity.
A galectin-3 (Gal-3) immunohistochemical stain was performed, which was negative.
The presence of a fibrous capsule and traversing thick, hyalinised fibrous bands seen in this case are not usually seen within a regular parathyroid adenoma and are a noted feature of atypical parathyroid adenoma, along with a solid and trabecular growth pattern and scattered mitotic figures.
Parathyroid carcinoma vs atypical parathyroid adenoma
The definitive diagnosis of parathyroid carcinoma is the presence of metastatic disease or localised invasion into surrounding structures. Histological features of parathyroid carcinoma include:
- capsule invasion and involvement of surrounding structures
- lymphovascular/perineural invasion
- elevated mitotic rate with atypical mitotic figures
Atypical parathyroid adenoma
Atypical adenomas lack the definitive evidence of parathyroid carcinoma but display some abnormal features:
- thick hyalinised fibrous bands
- incomplete capsular invasion
- prominent trabecular growth pattern
- necrosis (real, tumour-associated necrosis)
- increased mitotic rate (>1/10hpf) - uncommon
Note: Adenomas likely need to show more than just one abnormal feature to be designated as 'atypical', with some suggesting 2+ to qualify for a diagnosis.
PTH is a great stain to determine the parathyroid nature of the cells. There are not any definitive or diagnostic immunohistochemical stains you can use to distinguish between benign and malignant (or potentially malignant) parathyroid neoplasms, however, the following have been used in research settings:
Adenoma (vs 'normal'): neurofilament, GFAP, vimentin, less intense PTH and chromogranin
Parathyroid Carcinoma: Ki67, galectin-3, cyclin D1, bcl2, MDM2
- Rodriguez C, Nadéri S, Hans C, Badoual C Parathyroid carcinoma: A difficult histological diagnosis. Eur Ann Otorhinolaryngol Head Neck Dis. 2012 Jun;129(3):157-9 (open/free access) http://www.sciencedirect.com/science/article/pii/S1879729612000348
- Carlson D. Parathyroid pathology: hyperparathyroidism and parathyroid tumors. Arch Pathol Lab Med. 2010 Nov;134(11):1639-44 (open/free access) http://www.archivesofpathology.org/doi/pdf/10.1043/2009-0578-CCR.1