Introduction
Parathyroid cysts (PCs) are rare, constituting less than 0.5% of parathyroid lesions. PCs are often asymptomatic or present with non-specific symptoms, posing challenges for accurate diagnosis.
Case Presentation
A 22-year-old female with no medical or surgical history presented for pre-operative assessment of a painless, growing left cervical mass. The patient had no symptoms of dysphagia, dyspnea, voice changes, or urolithiasis. Physical examination revealed a firm, mobile mass. Serum calcium, thyroid stimulating hormone (TSH), and parathyroid hormone (PTH) levels were normal.
Imaging Findings
A contrast-enhanced neck computed tomography (CT) scan was first performed demonstrating a cystic mass of the anterior upper mediastinum, developed under the left lobe of the thyroid gland displacing laterally the main carotid arteries without signs of invasion (Figure 1). The mass caused a right-sided displacement of the trachea without luminal stenosis and backward displacement of the esophagus without apparent communication (Figure 2). There was a normal thymic remnant which appeared to be at a distance from the cystic lesion. There were no abnormalities along the midline path of the thyroglossal duct (Figure 3). Magnetic resonance imaging (MRI) confirmed the purely cystic nature of the lesion (Figure 4). An ultrasound (US) using a high-resolution linear probe (18 MHz) and a micro convex probe (12 MHz) was performed for further evaluation. It showed a well-defined extrathyroid homogeneous cystic lesion (Figure 5). The thyroid was of normal size and echogenicity raising the suspicion of a PC.
Discussion
Background
PCs are a rare entity representing less than 0.5% of parathyroid glands’ pathologies and account for 1%-5% of neck masses [1]. They can be found from the angle of the mandible until the mediastinum and are divided into two categories: functioning and non-functioning [1]. PCs seem to have a female predilection with a male: female ratio 1:2.5 [2]. The majority of PCs arise from the inferior parathyroid gland [3,4].
Clinical perspective
PCs can be asymptomatic or show several symptoms such as neck swelling or lump, neck pain, dyspnea, dysphagia, hoarseness, and signs of hyperparathyroidism [5-9]. Due to their non-specific symptoms and overlapping radiographic features with other neck masses, accurate diagnosis can be challenging.
Imaging perspective
The initial evaluation of a cystic neck mass should include a thorough history, physical examination, and imaging studies. The US remains a valuable method for accurate diagnosis of PCs. US-guided fine needle aspiration cytology (FNAC) can aid in the diagnostic approach by analyzing the cystic fluid composition and in situ PTH levels. In our case, a US-guided FNAC was performed revealing clear fluid that was sent to a laboratory for cytologic examination and in situ dosage of thyroglobulin (TG) and PTH (Figure 6) levels. The cytologic examination confirmed the cystic nature of the lesion. In situ TG level was negative, ruling out the diagnosis of thyroid cyst (TC). In situ PTH level was high (314 ng/l) and serum PTH level was normal. The diagnosis of a non-functioning PC is confirmed. The surgical approach was then canceled and replaced by US-guided cyst aspiration relieving the symptoms of the patient.
Contrast-enhanced sagittal CT scan showing no abnormalities along the path of the thyroglossal duct.
Outcome
Once a PC is diagnosed, the management should be individualized based on the patient’s symptoms. Asymptomatic, small non-functioning cysts can be managed conservatively. However, larger symptomatic or functioning cysts warrant aspiration, alcohol sclerotherapy, or surgical intervention [8]. Intraoperative monitoring of PTH levels is a valuable tool to confirm the successful removal of the PC [8].
Teaching Points
TCs are the most common differential diagnosis of non-functioning PCs [1]. FNAC and in situ dosage of TG/PTH levels can rule in or out the diagnosis.
Thyroglossal duct cysts are to be considered in the presence of a typical midline cystic mass that moves with swallowing or tongue protrusion. In this case, consider FNAC and in situ dosage of TG.
Suspicious thyroid nodules or a history of malignancy should raise the suspicion of cystic lymphadenopathy.
Branchial cleft cysts occur in younger individuals and are located along the anterior border of the sternocleidomastoid muscle [1].
A lymphatic malformation can also present as a cystic neck mass typically in childhood and can cause compressive symptoms [10].