Parathyroid adenoma

Epidemiology and Etiology:

• All age groups
• 50-60y peak
• F:M = 3:1

Common sites:

• In proximity to the thyroid
• ectopic sites:
• mediastinum
• lingual

Gross features:

• almost always solitary
• other parathyroid glands should be normal size or shrunken
• 0.5-300g (most 0.2-1.0g)
• well-circumscribed
• soft
• tan to reddish-brown
• yellow-brown rim of normal gland tissue (50-60%)

Histologic features:

• delicate capsule
• rim of compressed, non-neoplastic parathyroid tissue, outside of capsule
• uniform, polygonal chief cells with small, centrally-placed nuclei
• chief cell adenoma
• follicular architecture may be seen
• may have bizarre, pleomorphic nuclei
• mitoses unhelpful, but usually < 1 per 10HPF
• a few nests of larger oxyphil cells
• uncommonly may comprise the entire adenoma (oxyphil adenoma)
• inconspicuous adipose tissue within adenoma (in contrast to normal parathyroid)
• background of hyperplasia suggests MEN 1
• oxyphil adenoma:
• composed entirely of oxyphil cells
• massive infarction may occur (spontaneous or following FNA, may be associated with hypercalcemic crisis)
• lipoadenoma
• lots of fat with only scattered nests, cords, anastomosing trabeculae of chief cells
• may be a hamartoma

Immunophenotype:

Marker:	Sensitivity:	Specificity:
PTH
Chromogranin A
Argyrophil reaction
LMWK
TTF-1 (neg)
MIB-1 (usually <=5%)

Molecular features:

•  sporadic:
• PRAD1/PTH translocations (10-20%)
1. pericentromeric inversion putting PRAD1 (encoding cyclin D1) in the transcriptional regulation of PTH
• Cyclin D1 overexpression (40%)
• MEN1 mutations to both copies (10-20% of sporadic)
• Familial:
• MEN 1 (background of hyperplasia)
• Cytogenetics:
• Losses of 1p/q, 6q, 11 (11q23 and 11q13/MEN1), 13q, 15q

Other features:

References:

•  Robbins & Cotran Pathologic Basis of Disease (2005)
• WHO Tumours of Endocrine Organs (2004)