Answer to Quiz No. 20/2015 dated 12 July 2015
Pyramidal lobe of thyroid
Findings
Well defined lesion which follows thyroid signal intensity is seen in left omohyoid muscle in the left paramedian location. Heterogeneous enhancement is observed on contrast imaging. On T1w and T2w: hyperintense to skeletal muscles. T1w post contrast:shows heterogenous enhancement.
Discussion
The pyramidal lobe of thyroid is a normal anatomical variant of the thyroid gland. It is likely related to a remnant of the thyroglossal duct and is vestigial thyroid tissue. incidence : present in 10-30% of the population. It usually arises from the isthmus upwards along the midline or is shifted towards the left of the neck, and is usually located anterior to the thyroid cartilage(1). thyroid embryology:The thyroid primordium descends in the midline of the neck. The thyroid primordium first courses anteriorly to the primordial hyoid bone and then loops inferiorly and posteriorly to the hyoid bone before continuing its descent into the infrahyoid portion of the neck, anterior to the thyrohyoid membrane, thyroid cartilage, and trachea(2). Diagnosis: Scintigraphy, using Tc-99m, I-131, or I-123, is the most important diagnostic tool to detect ectopic thyroid tissue and shows the absence or presence of thyroid in its normal location. Radiological imaging modalities, such as grayscale or color Doppler US, computed tomography (CT), and magnetic resonance imaging (MRI), may help in designating the extension and location of ectopic tissue, thus contributing to a better pre-surgical evaluation(3) . On T1-weighted MR images, Pyramidal lobe of thyroid tissue is typically isointense to mildly hyperintense compared with the musculature, and on T2-weighted MR images, is mildly hyperintense, with variable enhancement after administration of a gadolinium-based contrast agent. THE IMPORTANCE OF THE PYRAMIDAL LOBE:The pyramidal lobe is of great importance to the thyroid surgeon . First, when performing total thyroidectomy for Graves’ disease, it is crucial to look for, identify, and remove the pyramidal lobe, as this can be a cause of recurrent hyperthyroidism following an incomplete resection of the gland. Second, it can be the site of origin of a thyroid cancer or contain intraglandular metastasis or multifocal disease, especially in cases of Papillary Carcinoma.
References
1.Practical Head and Neck Ultrasound. Greenwich Medical Media. (2000) ISBN:1900151995.
2.David A. Zander, MD, Wendy R. K. Smoker, MD, From the Department of Radiology, University of Iowa Hospitals and Clinics, 200 Hawkins Dr, Iowa City, IA 52242.Imaging of Ectopic Thyroid Tissue and Thyroglossal Duct Cysts. radiographics January-February 2014 Volume 34, Issue 1.
3.Ectopic thyroid tissue: anatomical, clinical, and surgical implications of a rare entity George Noussios ET AL Ectopic thyroid tissue: anatomical, clinical, and surgical implications of a rare entity Eur J Endocrinol 165 375-382, doi: 10.1530/EJE-11-0461 First published online 29 June 2011.
Contributed By:
Dr. Ravikanth Balaji, Dr.Jeyaraj Govindaraj , Dr. Bagyam Raghavan, Dr.Padmanabhan, Dr.Raghavendra, Apollo speciality hospitals, Teynampet, Chennai
Findings
Well defined lesion which follows thyroid signal intensity is seen in left omohyoid muscle in the left paramedian location. Heterogeneous enhancement is observed on contrast imaging. On T1w and T2w: hyperintense to skeletal muscles. T1w post contrast:shows heterogenous enhancement.
Discussion
The pyramidal lobe of thyroid is a normal anatomical variant of the thyroid gland. It is likely related to a remnant of the thyroglossal duct and is vestigial thyroid tissue. incidence : present in 10-30% of the population. It usually arises from the isthmus upwards along the midline or is shifted towards the left of the neck, and is usually located anterior to the thyroid cartilage(1). thyroid embryology:The thyroid primordium descends in the midline of the neck. The thyroid primordium first courses anteriorly to the primordial hyoid bone and then loops inferiorly and posteriorly to the hyoid bone before continuing its descent into the infrahyoid portion of the neck, anterior to the thyrohyoid membrane, thyroid cartilage, and trachea(2). Diagnosis: Scintigraphy, using Tc-99m, I-131, or I-123, is the most important diagnostic tool to detect ectopic thyroid tissue and shows the absence or presence of thyroid in its normal location. Radiological imaging modalities, such as grayscale or color Doppler US, computed tomography (CT), and magnetic resonance imaging (MRI), may help in designating the extension and location of ectopic tissue, thus contributing to a better pre-surgical evaluation(3) . On T1-weighted MR images, Pyramidal lobe of thyroid tissue is typically isointense to mildly hyperintense compared with the musculature, and on T2-weighted MR images, is mildly hyperintense, with variable enhancement after administration of a gadolinium-based contrast agent. THE IMPORTANCE OF THE PYRAMIDAL LOBE:The pyramidal lobe is of great importance to the thyroid surgeon . First, when performing total thyroidectomy for Graves’ disease, it is crucial to look for, identify, and remove the pyramidal lobe, as this can be a cause of recurrent hyperthyroidism following an incomplete resection of the gland. Second, it can be the site of origin of a thyroid cancer or contain intraglandular metastasis or multifocal disease, especially in cases of Papillary Carcinoma.
References
1.Practical Head and Neck Ultrasound. Greenwich Medical Media. (2000) ISBN:1900151995.
2.David A. Zander, MD, Wendy R. K. Smoker, MD, From the Department of Radiology, University of Iowa Hospitals and Clinics, 200 Hawkins Dr, Iowa City, IA 52242.Imaging of Ectopic Thyroid Tissue and Thyroglossal Duct Cysts. radiographics January-February 2014 Volume 34, Issue 1.
3.Ectopic thyroid tissue: anatomical, clinical, and surgical implications of a rare entity George Noussios ET AL Ectopic thyroid tissue: anatomical, clinical, and surgical implications of a rare entity Eur J Endocrinol 165 375-382, doi: 10.1530/EJE-11-0461 First published online 29 June 2011.
Contributed By:
Dr. Ravikanth Balaji, Dr.Jeyaraj Govindaraj , Dr. Bagyam Raghavan, Dr.Padmanabhan, Dr.Raghavendra, Apollo speciality hospitals, Teynampet, Chennai