Thyroid & parathyroid

Parathyroid nonmalignant

Parathyroid adenoma

Editorial Board Member: Andrey Bychkov, M.D., Ph.D.
Editor-in-Chief: Debra L. Zynger, M.D.

Last author update: 27 October 2020
Last staff update: 10 May 2023

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PubMed Search: Parathyroid adenoma[TIAB] pathology[title]

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Cite this page: Lin DM. Parathyroid adenoma. website. Accessed June 8th, 2023.
Definition / general
  • Benign neoplasm derived from parathyroid parenchymal cells
  • Typically involves one gland
Essential features
  • Incidence increasing due to biochemical testing
  • Diagnosis confirmed by a drop in parathyroid hormone (PTH) after surgical removal
  • Atypical parathyroid adenoma displays histology concerning for but not diagnostic of malignancy and requires clinical follow up after excision
  • Can be mistaken for thyroid follicular neoplasm by fine needle aspiration
ICD coding
  • ICD-10: D35.1 - Benign neoplasm of parathyroid gland
  • Parathyroid gland, inferior glands slightly more common than superior
  • Can also occur where ectopic / supernumerary parathyroid tissue may be found (thyroid gland, thymus, retroesophageal area, mediastinum, vagus nerve, carotid sheath)
  • Double adenomas can occur, usually involving both superior parathyroid glands (Surg Pathol Clin 2019;12:1007)
Clinical features
  • Often detected early in asymptomatic patients due to routine serologic testing (see laboratory findings below)
  • Symptoms of hyperparathyroidism: nephrolithiasis, osteopenia, osteitis fibrosa cystica, weakness, fatigue and psychiatric disturbances can occur if not detected early
  • Rarely presents as a palpable mass (J Med Case Rep 2019;13:332)
  • Various imaging techniques can identify parathyroid nodules, including CT, MRI and ultrasound
  • Technetium 99 sestamibi scintigraphy (99mTc) (see radiology description below)
  • Intraoperative parathyroid hormone (PTH) rapidly decreases after the abnormal gland is removed
Radiology description
  • Nodule posterior to thyroid gland
  • 99mTc sestamibi:
    • Sestamibi accumulates in the mitochondria rich oxyphil cells of the parathyroid
    • Increased focal uptake may indicate an adenoma (J Nucl Med 1992;33:1801)
Radiology images

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99mTc MIBI scintigraphy

Prognostic factors
  • Normally can be cured by surgical removal but recurrences can happen if not properly localized and excised
  • Atypical adenomas are considered tumors of uncertain malignant potential and should be followed up clinically (Surg Pathol Clin 2019;12:1007)
Case reports
  • Parathyroidectomy
Clinical images

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Giant parathyroid adenoma (intraoperative)

Gross description
Gross images

Contributed by Mona Kandil, M.D.

Parathyroid adenoma (black arrow) and thyroid

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Right: parathyroid adenoma;
left: thymoma

Frozen section description
  • Identification of parathyroid tissue is usually sufficient for intraoperative management, rather than trying to distinguish adenoma from hyperplasia
Microscopic (histologic) description
  • Well circumscribed, frequently with thin fibrous capsule
  • Absent or reduced stromal adipocytes
  • Compressed nonneoplastic parathyroid tissue may be seen at edge
  • Most commonly composed of chief cells (round nucleus, little granular cytoplasm)
  • Follicle formation is not rare
  • Mitoses and bizarre nuclei (endocrine atypia) may be focally present
  • Variants:
    • Oxyphilic / oncocytic adenomas: composed entirely of oncocytic cells with abundant, eosinophilic granular cytoplasm (Surg Pathol Clin 2019;12:1007)
    • Water clear cell adenoma: cells have clear, glycogen containing cytoplasm (Surg Pathol Clin 2019;12:1007)
    • Lipoadenoma (hamartoma): contains stromal (adipose) and parenchymal (usually chief cells) elements; most of the tumor is adipose tissue (Surg Pathol Clin 2019;12:1007)
    • Atypical adenoma: contains borderline features concerning for (but not diagnostic of) malignancy (Surg Pathol Clin 2019;12:1007)
      • Dense fibrous bands with hemosiderin
      • Prominent nuclear atypia with spindled nuclei
      • Notable mitotic activity
      • Adherence to adjacent tissue
      • Necrosis
      • Solid or trabecular growth
      • No evidence of lymphovascular invasion, perineural invasion, invasion into adjacent structures or metastasis
Microscopic (histologic) images

Contributed by Diana Murro Lin, M.D.

Chief cells

Oxyphil adenoma

Oxyphil cells

Atypical adenoma and thyroid

Atypical adenoma fibrous bands

Virtual slides

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Parathyroid adenoma

Cytology description
  • Cellular aspirates with uniform small cells in sheets, 3D clusters and trabecular arrangements
  • Round dark nuclei with smooth nuclear borders and without nucleoli
  • Salt and pepper chromatin (Diagn Cytopathol 2020 Aug 24 [Online ahead of print])
  • No colloid unless adjacent thyroid tissue is also aspirated
  • More monotony than normal thyroid tissue
  • Can be mistaken for a thyroid follicular neoplasm (Diagn Cytopathol 2017;45:526)
Cytology images

Contributed by Ayana Suzuki, C.T.

Sheet of chief cells

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Microfollicular and trabecular arrangement

Electron microscopy description
Molecular / cytogenetics description
  • CDC73 (HRPT2) in patients with hyperparathyroidism jaw tumor syndrome (Endocr Pathol 2018;29:113)
  • MEN1 in multiple endocrine neoplasia and sporadic adenomas
  • For fine needle aspiration samples, the Veracyte Afirma Gene Expression Classifier contains a cassette to distinguish parathyroid from thyroid tissue (Diagn Cytopathol 2017;45:526)
  • Mutations in CCND1 (cyclin D1), ZFX, EZH2 (Surg Pathol Clin 2019;12:1007)

Oncocytic adenoma

Parathyroid pathology

Sample pathology report
  • Right lower parathyroid, parathyroidectomy:
    • Chief cell adenoma, 250 mg
Differential diagnosis
Board review style question #1

What is the best diagnosis for this neck mass?

  1. Parathyroid adenoma, oxyphil type
  2. Oncocytoma
  3. Hurthle cell adenoma
  4. Granular cell tumor
Board review style answer #1
A. Parathyroid adenoma, oxyphil type

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Reference: Parathyroid adenoma
Board review style question #2
Which of the following features is seen in parathyroid carcinoma but not adenoma?

  1. Adherence to adjacent thyroid
  2. Nuclear atypia
  3. Necrosis
  4. Perineural invasion
Board review style answer #2
D. Perineural invasion

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Reference: Parathyroid adenoma
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