An Interesting Case of Atypical Parathyroid Adenoma: A Diagnostic and Management Conundrum

Presentation Number: MON 323
Date of Presentation: April 3rd, 2017

Richa M Patel*, Randall Butler and Dima Lutfi Diab
University of Cincinnati, Cincinnati, OH

Abstract

Primary hyperparathyroidism (PHPT) affects 0.1-0.3% of the population and is due to a benign parathyroid adenoma 80-85% of the time. Parathyroid carcinoma (PC) and atypical parathyroid adenoma (APA) are exceptionally rare causes of PHPT (<1%). APA can have very similar clinical characteristics as PC making diagnosis and management difficult.

A 58-year-old male presents with a right neck mass, serum calcium (Ca) 16.5 mg/dL (8.6- 10.3), PTH 1233 pg/mL (12.0-88.0), phosphorus 2.0 mg/dL (2.1-4.7) and creatinine 1.38 mg/dL (0.6-1.30). He reported joint pain and mild memory loss. Thyroid ultrasound noted a heterogeneous, complex mass in the right thyroid lobe, 5.4 cm in largest dimension, with high concern for malignancy. Neck CT showed a 5.9 cm heterogeneous, predominantly hypodense lesion in the right thyroid lobe, with mass effect on the common carotid artery and trachea, and with no lymph node enlargement or distant lesions to suggest metastasis.

Intraoperatively, the mass was invading the esophagus and the recurrent laryngeal nerve could not be spared in order to expose the esophageal component of the mass. Intraoperative PTH was 161 pg/mL. Pathology showed a 4.2 cm encapsulated, soft, hemorrhagic nodule with a thick irregular capsule adherent to the thyroid gland, without transcapsular or intravascular invasion, most consistent with APA. Postoperatively, Ca and PTH levels normalized. No residual or recurrent mass was identified on subsequent neck CT.

Currently, there are no defined criteria for the diagnosis of APA. Carcinoma was high on our differential due to the degree of hypercalcemia and aggressive behavior of the lesion. Histology showed a thickened, irregular capsule adherent to the thyroid, fibrotic bands within the tumor, and intracapsular entrapment of parathyroid cells. There was no invasion of adjacent tissue, vasculature, lymphatics or nerves, which are the only criteria that can definitively indicate PC over APA. There are also no genetic tests or immunostains that can differentiate the two. The majority of cases of PC are due to HRPT2/CDC73 gene mutation on chromosome 1, but APA can also have the same mutation. Both APA and PC can also express immunohistochemical markers such as p27, bcl2, Ki-67, MDM2 and Parafibromin.

There are also no guidelines for long term APA surveillance or management. APA usually has a benign course and low recurrence. However, there is loss of similar gene loci in APA and PC which suggests that the molecular pathogenesis may be the same, and APA’s are described as parathyroid tumors with uncertain malignant potential. PC and APA have a clinically, intraoperatively and biochemically similar presentation. Definitive differentiation can only be based on histologic findings of local invasion or distant metastasis. Management and surveillance should be tailored to each patient. We will continue to monitor labs and neck imaging in our patient at least annually.

 

Nothing to Disclose: RMP, RB, DLD