Atypical presentations of parathyroid gland pathology: A pictorial review

Abstract

Primary hyperparathyroidism is associated with significant morbidity and mortality. It is in this day and age, an eminently treatable condition which relies heavily on preoperative imaging to localise enlarged parathyroid glands. The imaging appearances of parathyroid gland enlargement are varied; this paper seeks to address some of its more unusual manifestations with an emphasis on its atypical enhancement patterns, mimics and associations. An enlarged glands may also present as an 'incidentaloma' in head and neck imaging performed for entirely different indications, or as part of sporadic or familial syndrome. Radiologists are in a good position to expedite the relevant investigations and curative treatment, and knowledge of the spectrum of imaging appearances is crucial.

Keywords: Cystic parathyroid gland; Ectopic intrathyroidal parathyroid gland; Hyperparathyroidism jaw tumour syndrome; Non-Enhancing parathyroid glands; Parathyroid gland enlargement; Parathyroid gland haemorrhage.

Fig. 1

(a) Classic sonographic appearance and site of an enlarged right-sided parathyroid gland. These are often ovoid and hypoechoic relative to the thyroid parenchyma. Enlarged glands are often situated in a retro-thyroid location and it is important to describe the location(s) of potential candidate(s) in the radiology report (e.g. posterior to the mid-pole of the thyroid) to aid minimally-invasive parathyroidectomy and neck exploration. (b) Ultrasound image from a different patient. This is a partly-exophytic U3 (BTA classification) nodule located within the deep aspect of the right thyroid lobe. Both lesions appear similar at first glance however, the subtle fat plane (arrowed) separating thyroid and parathyroid tissue in (a) and not appreciated in (b) can serve as a useful distinguishing feature.

Fig. 2

Retropharyngeal parathyroid gland. (a) The Tc-99 m sestamibi study was originally reported as negative for parathyroid gland enlargement. (b) An avidly-enhancing focus within the retropharyngeal space at the level of the floor of the mouth (arrow) was described on subsequent CECT. Both sets of images were jointly reviewed by radiologists and nuclear medicine physicians in the endocrine multidisciplinary team meeting. Radiotracer retention on the delayed acquisitions (broken arrow) was identified retrospectively. This case highlights the importance of additional functional and cross-sectional studies for imaging concordance as ultrasound is notoriously limited in its ability to detect ectopic parathyroid tissue. Additionally, potential candidates for parathyroid gland enlargement may be easily overlooked if present in unusual locations or under/over-reported given that delayed Tc-99 m sestamibi washout can be seen in a variety of non-thyroid/parathyroid tissue.

Fig. 3

Axial pre and post-contrast CT images through the neck. The post-contrast images were acquired at 25 s following intravenous contrast administration to coincide with peak enhancement of parathyroid tissue. The images demonstrate the presence of an avidly-arterialising, hypervascular lesion within the left tracheo-oesophageal groove which was deemed to represent a good candidate for an enlarged parathyroid gland (solid arrows). The lesion is hyperattenuating relative to lymphoid tissue (broken arrow) and this differential enhancement is a useful distinguishing feature.

Fig. 4

(a) Axial CECT image demonstrates an enlarged parathyroid gland in the retrothyroid location (x) on the right. There is a further candidate in the mirror-image location within the contralateral neck medial to the left common carotid artery. (b) Coronal reformats better demonstrate a feeding artery (arrow) - this is usually a branch of the thyrocervical trunk.

Fig. 5

Cystic parathyroid gland. (a) Transverse ultrasound images through level VI demonstrate a cystic lesion (x) posterior to the lower pole of the left thyroid gland and (b) extending into level VII of the neck in a patient investigated for primary hyperparathyroidism. Posterior acoustic enhancement was evident and no solid components were identified. The radiologist was confident that this represented a functional parathyroid cyst however, the lower pole of the lesion was not visualised sonographically and CECT was performed for full assessment. (c) Coronal CECT confirms the presence of an enlarged, cystic parathyroid gland (<10HU in density).

Fig. 6

Ultrasound (a) and CECT (b) performed for the investigation of primary hyperparathyroidism. The images demonstrate an extra-thyroid, right-sided septated cystic-solid lesion within level VI of the neck and the arrow points to non-dependent, subtle intralesional soft tissue. There is effacement of the right pyriform fossa more superiorly. Fine needle aspiration was unfortunately non-diagnostic and this was subsequently confirmed as an enlarged parathyroid gland following resection and histology. Its complex appearances suggest cystic degeneration or prior haemorrhage into the gland. This case highlights the importance of requesting a parathormone assay at the same time as cytological analysis.

Fig. 7

(a) and (b) Sonographic assessment of the neck confirmed the presence of a multinodular goitre; there was marked and asymmetric enlargement and hyperplastic change on the left. A potential candidate for parathyroid gland enlargement was demonstrated on the right and a benign, dominant and partly-exophytic thyroid nodule described on the left. (c) Subtraction image from nuclear scintigraphy demonstrates concordance on the right but also raised the possibility of an enlarged left-sided parathyroid lesion. The suspicion of an intra-thyroid parathyroid gland on the left was corroborated on venous sampling.

Fig. 8

This patient underwent imaging after presenting to Accident and Emergency with rapid-onset dysphagia, neck and chest pain. (a) CECT (ENT soft tissue protocol) showed extensive retropharyngeal haematoma causing compression of the oesophagus and a peripherally-enhancing focus within the left para-oesophageal region. (b) and (c) The subsequent T1 post-contrast axial image showed a similar finding with layered hyperacute-acute blood products within the retropharyngeal space and better appreciated on the T2 sagittal image. The patient had no history of trauma or underlying coagulopathy to account for this. Follow up ultrasound study identified an enlarged parathyroid gland favouring a ruptured adenoma as the cause for the patient’s acute presentation.

Fig. 9

This patient presented to Accident and Emergency following chest pain and stridor. A large, hypoattenuating lesion was seen within the superior mediastinum on CECT. This was inseparable from the upper aerodigestive tract structures, and deviation and compression of the trachea and oesophagus was described. The initial differentials included an underlying lymphoproliferative disorder, bronchogenic malignancy and parathyroid carcinoma (given the abnormal calcium profile). This was resected following multidisciplinary discussion and histology confirmed a haemorrhagic, benign parathyroid adenoma. The apparent non/hypo-enhancement was due to intralesional haematoma.

Fig. 10

CECT and MRI images from a young woman undergoing screening for succinyl dehydrogenase (SDH) mutation. SDH mutations are germline mitochondrial defects which place patients at increased risk of developing multi-system neoplasms including paragangliomas in the head and neck region. In our institution, screening involves non-contrast whole body MRI (neck, thorax, abdomen and pelvis). (a) and (b) A left-sided carotid body tumour was found on CECT. (c) A millimetric hypervascular focus was seen in the right tracheo-oesophageal groove on the axial images. This was confirmed to represent an enlarged parathyroid gland on further assessment and this was found to be present on historic screening MR imaging; (d) parathyroid tissue is typically T2/STIR-hyperintense and (e) T1-isointense. These lesions can be difficult to detect due to their small size and similar signal characteristics to nodal tissue.

Fig. 11

Images from a different patient who underwent (a) sonographic and (b) scintigraphic assessment for primary hyperparathyroidism - these confirmed an enlarged parathyroid gland posterior to the upper pole of the left thyroid lobe. Review of prior MR images performed for SDH mutation screening revealed the presence of a cigar-shaped (c) T2/STIR-hyperintense and (d) T1-hypointense lesion (arrowed) which corresponded to the solitary, functional parathyroid adenoma.

Fig. 12

CECT performed for an intensive care patient who had been admitted with necrotising pancreatitis. (a) Imaging through the abdomen demonstrated extensive, loculated peripancreatic fluid collections and splenic vein thrombosis (arrow) complicated by hollow viscus perforation (broken arrow). An underlying parathyroid carcinoma was suspected as the serum calcium levels were found to be >10x the upper limit of normal. (b) Imaging through the neck and chest demonstrated a locally-invasive right-sided parathyroid carcinoma (confirmed on histology) invading the posterior tracheal wall and the posterolateral wall of the oesophagus. Note the very similar imaging appearances between this case and Fig. 10. Focal right upper lobe consolidation was also noted.

Fig. 13

NCCT (non-contrast CT) multiplanar reconstructions and 3D-rendering of a left mandibular non-ossifying fibroma. The expansile, lucent lesion has remodelled and thinned the mandibular buccal cortex. Whilst it is intimately related to the roots of LL6 and LL7, there is no associated root resorption.

Fig. 14

This is a more extreme case of hyperparathyroidism jaw tumour syndrome. (a) Multiplanar CT reconstructions and volume-rendered image demonstrate multiple craniofacial fibromas and significant facial deformity. There is extensive involvement of the maxilla and mandible, with varying degrees of intralesional matrix mineralisation seen. There is encroachment of the left orbital floor (arrow) with a resultant left-sided proptosis. A tracheostomy is in situ. (b) An enlarged parathyroid gland was seen on coronal reformats (broken arrow).