Multi-modality parathyroid imaging: A shifting paradigm

Table 1 Differentiating features of parathyroid adenoma from lymph nodes and thyroid nodules on imaging

Modality	Features	Parathyroid adenoma	Thyroid nodule	Lymph node
USG	Echogenicity	Homogenously markedly hypoechoic	Homo/Heterogenously hypo/isoechoic	Central echogenic hilum
	Vascularity	Peripheral polar vessel sign present	Not seen	Central/hilar vascularity
	Calcification	Less common	Common	+/-
	Cystic changes	Less common	More common	+/-
CT	Non contrast	Hypodense	Hyperdense	Hypodense
	Arterial	Intense arterial enhancement	Enhancement in arterial phase but less than parathyroid adenomas	No enhancement in the arterial phase
	Venous	Washout	Persistent enhancement	Progressive enhancement in venous phase
MRI	Morphology	Cleavage plane with thyroid gland	No cleavage plane	Cleavage plane present
	Diffusion weighted Image	High SI		High SI
PET Choline	Uptake	Present	Variable	Uptake may be present, however is delayed and of lesser intensity

USG: Ultrasound; CT: Computed tomography; MRI: Magnetic resonance imaging; SI: Signal intensity; PET: Positron emission tomography.

Table 2 Differentiating features of various parathyroid lesions

	Parathyroid hyperplasia	Parathyroid adenoma	Parathyroid carcinoma
USG	Small; Ovoid; Well-circumscribed; Homogenously hypoechoic; Calcifications uncommon; No local invasion; CEUS - Homogeneous enhancement	Small; Ovoid; Well-circumscribed; Homogenously hypoechoic; Calcifications uncommon; No local invasion; CEUS - Peripheral enhancement with central washout on delayed image	Large; Irregular shape; Non circumscribed margins; Heterogenous echotexture; Intra-nodular calcifications; Local invasion
CT	Small hypodense lesion (as compared to thyroid gland); Intense arterial enhancement; Washout on the venous phase; May not be identifiable on CT	Small hypodense lesion (as compared to thyroid gland); Intense arterial enhancement; Washout on the venous phase	Lesions may show infiltration into the surrounding structures
MRI	Small sized; Well defined; Homogenous;Low on T1; High on T2; Avid enhancement	Small sized; Well defined; Homogenous;Low on T1; High on T2; Avid enhancement	Large; Ill-defined; Heterogenous

USG: Ultrasound; CT: Computed tomography; MRI: Magnetic resonance imaging; CEUS: Contrast enhanced ultrasound.