Cystic parathyroid adenoma mimicking thyroid adenoma: A rare case with review of literature

Arockia Silviya Irene; Krishna Biswas; Shivani Paruthi; Ashish K Mandal

doi:10.4103/trp.trp_24_17

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CASE REPORT

Year : 2017 | Volume : 14 | Issue : 3 | Page : 124-126

Cystic parathyroid adenoma mimicking thyroid adenoma: A rare case with review of literature

Arockia Silviya Irene¹, Krishna Biswas¹, Shivani Paruthi², Ashish K Mandal³
¹ Department of Endocrinology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
² Department of Surgery, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
³ Department of Pathology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India

Date of Web Publication

9-Oct-2017

Correspondence Address:
Arockia Silviya Irene
F 102, First Floor, Ansari Nagar West, New Delhi - 110 049
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/trp.trp_24_17

Abstract

Parathyroid cyst is one of the rare differential diagnosis of cystic neck mass. It is often mistaken as a thyroid swelling. Functional parathyroid cyst secretes parathyroid hormone producing hypercalcemia. Here, we report a case of cystic parathyroid adenoma, which was mistaken as thyroid adenoma and operated upon. Reevaluation of the pathology specimen has given clue to the presence of parathyroid tissue. Ultrasonographic evaluation of cystic neck lesion by experienced radiologist and technetium 99m sestamibi scan helps in the diagnosis. Biochemical evaluation for hyperparathyroidism should be done in all such suspected cystic neck lesion as they may be asymptomatic for hypercalcemia.

Keywords: Cystic neck mass, cystic parathyroid adenoma, thyroid adenoma

How to cite this article:
Irene AS, Biswas K, Paruthi S, Mandal AK. Cystic parathyroid adenoma mimicking thyroid adenoma: A rare case with review of literature. Thyroid Res Pract 2017;14:124-6

How to cite this URL:
Irene AS, Biswas K, Paruthi S, Mandal AK. Cystic parathyroid adenoma mimicking thyroid adenoma: A rare case with review of literature. Thyroid Res Pract [serial online] 2017 [cited 2021 Jan 25];14:124-6. Available from: https://www.thetrp.net/text.asp?2017/14/3/124/216209

Introduction

Primary hyperparathyroidism is a primary abnormality of parathyroid gland leading to inappropriate secretion of parathyroid hormone (PTH). 80%–85% of such cases are due to parathyroid adenomas and 15%–20% are due to hyperplasia. Cystic diseases of the parathyroid glands is a rare finding, accounting for <0.01% of neck masses.^[1] So far, about 300 cases of cystic parathyroid adenomas have been reported in literature.^[2] Although different diagnostic modalities are available for symptomatic parathyroid adenomas, accurate preoperative diagnosis of asymptomatic cystic parathyroid adenoma is generally difficult.

Case Report

AA, a 44-year-old female, was having asymptomatic right-sided neck swelling for 3 years. She had undergone subtotal thyroidectomy outside for recent increase in size of the swelling. The histopathology report was suggestive of follicular adenoma of thyroid with cystic and hemorrhagic changes. However, since the swelling persisted even after surgery, she attended our hospital. On clinical examination, the significant finding was a well-defined firm swelling 2 cm × 1 cm on the right side of the neck, moving with deglutition. There was a single horizontal scar of 10 cm in the neck. Block of the surgical specimen reviewed in our hospital showed features suggestive of parathyroid adenoma. Hence, we started working up for evidence of hyperparathyroidism. Clinically, there were no symptoms or signs suggestive of hyperparathyroidism. The pertinent investigations done were serum free thyroxine - 10.6 mcg/dl, serum thyrotropin - 2.16 mIU/L, serum calcium - 10.2 mg/dl, serum phosphorus - 2.7 mg/dl, serum alkaline phosphatase - 257 IU/l, serum creatinine - 0.6 mg/dl, serum PTH - 224.6 pg/ml, and serum 25-hydroxy Vitamin D₃- 28.75 ng/ml. Ultrasonogram (USG) of the neck showed upward displacement of the right lobe of thyroid by a septated cystic mass measuring 16.4 mm × 16.3 mm × 15.44 mm inseparable from an irregular heterogeneous area measuring 69 mm × 86 mm [Figure 1]. Computed tomography (CT) neck showed the presence of an elongated cystic lesion with solid component and enhancing septations, abutting lower pole of the right lobe of thyroid [Figure 2]. Technetium-99m sestamibi parathyroid scan showed an abnormal tracer concentration in the region below lower pole of the right lobe of thyroid gland suggesting a right lower parathyroid adenoma [Figure 3].

Figure 1: Ultrasonogram neck: The right lobe of thyroid displaced up and to right by a separate cystic mass, 16.4 mm × 16.3 mm × 15.4 mm, inseparable from a heterogeneous area measuring 69 mm × 86 mm

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Figure 2: Computed tomography scan neck: An elongated 3.8 cm × 2.6 cm × 1.6 cm cystic lesion (black arrow) with solid component and enhancing septations noted abutting the lower pole of the right lobe of thyroid. Note the brightly enhancing normal thyroid (white arrow)

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Figure 3: Technetium 99m sestamibi parathyroid scan: showing right lower parathyroid adenoma

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She was referred to surgery for excision of adenoma. Intraoperative finding consisted of a lobulated cystic swelling in the region of the right lower parathyroid. The normal appearing right upper parathyroid was preserved. The excised mass measured 4 cm × 2.5 cm × 1 cm. Histopathology confirmed the presence of parathyroid adenoma [Figure 4]. Her PTH was <3 pg/ml in the immediate postoperative period. Postoperative hypocalcemia was treated with I.V followed by oral supplementation of calcium and alfacalcidol. The patient has been on follow-up for the last 1 year with supplementation of 1.5 g of elemental calcium daily.

Figure 4: Histopathology (Magnification-10X): A large tumor with sheets of clear, monomorphic cells without mitosis. Well encapsulated by fibro-collagenous tissue wherein, at the periphery of the capsule, compressed normal parathyroid could be identified. The compressed tissue is atrophic and is present in streaks/linear pattern. Outside this muscle and fibrous tissue and a part of thyroid could be identified

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Discussion

In 1880, Swedish anatomist Sandstrom reported the first case of parathyroid cyst.^[3] Cystic parathyroid lesions are uncommon and are rarely diagnosed before surgery. Most cystic parathyroid adenomas are located in the neck, about 10% are found in the mediastinum.^[1] Patients usually present with asymptomatic, smooth, nontender, solitary neck masses at the inferior border of thyroid-simulating a thyroid nodule.^[4],[5] Etiology of formation of parathyroid cysts is not clear. Parathyroid cysts may arise from vestigial remnants of third or fourth branchial clefts or the Kursteiner canals. It may also be formed by accumulation of fluid in the parathyroid gland or by degeneration of an adenoma or carcinoma.^[1] Cysts are classified as functional and nonfunctional depending on the presence or absence of hypercalcemia, respectively. Most parathyroid cysts are nonfunctional while functional cysts constitute only 10%–15% of all reported cases. The peak incidence of parathyroid cysts occurs between the fourth and sixth decade of life. While nonfunctional cysts are said to be common in females, functional cysts are found more commonly in males.^[6] Nonfunctional cysts are often diagnosed while investigated for producing compressive symptoms. Functional cysts, derived from adenomas that undergo central necrosis and degeneration account for 1% of all cases of hyperparathyroidism.^[7] Most of the patients with functional cysts have clinical features suggestive of primary hyperparathyroidism and may produce hypercalcemic crisis. However, in a few asymptomatic cases, there is only abnormality in serum calcium and phosphorus or elevated serum PTH.^[8]

USG features of parathyroid adenoma are well documented as homogeneously hypoechoic to the overlying thyroid measuring more than 1 cm.^[8] However, USG findings of cystic parathyroid adenomas have been limited to sporadic case reports and small surgical series. USG usually show a smooth-walled anechoic lesion with good through-transmission of sound, suggesting a cystic lesion.^[5] In general, there is no internal structure though septation or loculation may be found.^[9] In one study, 93% of cystic adenomas were elongated with peripheral solid component, were situated deep and inferolateral to adjacent thyroid, and in 60% cases, there is an echogenic border separating the adenoma from the thyroid. In 71% cases, color Doppler showed feeding vessels with internal color flow to the solid components. Combined with sestamibi scan the accuracy of preoperative localization was found to be 79%.^[10] Our patient also had an elongated cystic lesion with solid component and internal septations as evidenced in CT scan. Technetium-99m sestamibi parathyroid scan confirmed the presence of the right lower parathyroid adenoma in our case. At times, it is difficult to distinguish parathyroid cysts from other cystic lesions of the neck, for example, thyroid cyst, thyroglossal duct cyst, and branchial cleft cyst even after all radiological investigations. In such a situation, aspiration of the cyst fluid gives a clue to the diagnosis. Thin, clear, and colorless fluid with high PTH level is pathognomonic of parathyroid cyst.^[11] However, high PTH level is also present in nonfunctional parathyroid cyst. Nonfunctional cysts are amenable to treatment by aspiration or injection of sclerosing agents. Functional cysts should be subjected to surgical excision.^[2],[6]

Our patient underwent hemithyroidectomy for a supposedly thyroid swelling in another hospital. The histopathology slide review done in our setup was suspicious of a parathyroid adenoma, which prompted us to investigate her for hyperparathyroidism though she was asymptomatic. One similar case has been reported where posttotal thyroidectomy diagnosis was made as histopathology showed inner layer of the cyst consisting mainly of compressed chief parathyroid cells.^[2] Hence, providing clinical and radiological background to an expert pathologist is important in all cases of thyroidectomy at the time of histopathology study.

Conclusion

Cystic parathyroid adenoma though rare should always be considered as a differential diagnosis in any cystic lesion in the region of thyroid. Clinical evaluation for primary hyperparathyroidism should be done in all such cases. Ultrasound feature of a deep-seated, elongated cystic lesion with a solid component with echogenic borders separating it from thyroid favors the diagnosis of parathyroid cyst. Technetium-99m sestamibi parathyroid scan is advisable to confirm. Biochemical evaluation of serum calcium and PTH level, clear watery fluid in the aspirate with increased PTH in the aspirate help in definitive diagnosis.

Acknowledgment

The authors would like to thank Dr. Ritika Singh, M.D, Department of Pathology, Vardhman Mahavir Medical College, Safdarjung Hospital, New Delhi.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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