Two Brief Case Studies

Case 1:

A 6-year-old boy presents with a paramedian neck swelling at the level of the thyroid gland. It is only mobile during deglutition and not when sticking out the tongue. Ultrasound (fig. b) shows a cyst at the level of the isthmus with normal thyroid lobes. The patient’s thyroid hormone levels are normal.

Caption: a. Presentation of swelling b. Ultrasonographic. Sagittal T2 MRI.

Discussion

Diagnosis: Thyroglossal Duct Cyst.

The thyroid gland develops from the endoderm of the 2nd pharyngeal arch. More specifically, it buds from the floor of the primitive pharynx and descends passively. The tongue and the thyroid are connected by the thyroglossal duct, which degenerates by the 10th week. In 50% of cases, the distal portion of the duct forms the pyramidal lobe of the thyroid. In the case of Thyroglossal Duct Cysts, disintegration of the duct does not occur and secretions from the epithelial lining result in inflammation and cyst formation.

Source

The cyst can take on various positions, as shown by the figure above. There are a higher number of cases of cysts found at the level of the hyoid. Additionally, there is a risk of infection in children with patent thyroglossal ducts. Previously, management was by draining the cyst; however, due to recurrences, surgical excision of the entire duct and associated tissue is now the standard - the Sistrunk procedure (named after Walter Sistrunk).

(Case taken from: https://doi.org/10.1016/j.ejenta.2011.03.001)

Case 2:

A middle-aged woman presents to the GP due to an episode of sudden vertigo, left ear tinnitus and right arm weakness and numbness. She did not recall signs or symptoms suggestive of deep vein Thrombosis and did not satisfy any Wells’ criteria (for pulmonary embolism risk assessment). Vital signs were normal. Neurological examination disclosed a positive Romberg test, normal Weber and Rinne tests and no other neurological deficits. A Flair MRI, and transesophageal echocardiography were performed. Heart sounds were dual with no murmurs. She presented with mild but controlled dyslipidemia. Family history shows that her father suffered from myocardial infarction at 58 years.

Caption: Results of transesophageal echocardiography, where an agitated saline bubble study is used to examine for defects in the heart chambers and great vessels. Click here for a detailed demonstration

Caption a: MRI from the case

Caption b: Comparison between different types of MRI. FLAIR (Fluid-attenuated inversion recovery) MRI darkens Cerebrospinal fluid signals. With this technique, lesions situated near CSF can be clearly distinguished.

Discussion

Diagnosis: Let us first explore the different results.
The patient experienced a cryptogenic stroke. Defined as a stroke with ‘cryptic’ or unknown causes. This affects around 30%–40% of ischemic stroke patients.

The MRI shows infarction of the superior portion of the right cerebellum. This is consistent with the vertigo and tinnitus experienced by the patient.

The agitated saline bubble study indicated the presence of an interatrial septal defect, associated with a patent foramen ovale PFO. This is our culprit. A PFO can disrupt blood flow, which could result in thrombus formation. The thrombus then enters systemic circulation by moving into the left atrium. PFO remains an important aetiology to consider in cases of cryptogenic stroke, it is responsible for 42% of cryptogenic strokes in patients younger than 55 years and 15% in patients over 55 years of age.

Alternatively, in cases of deep vein thrombosis (which is not applicable here), a thrombus forming in the limbs can bypass pulmonary circulation (where it would usually cause pulmonary embolism) via the PFO into the systemic circulation, where it can cause occlusion of cerebral vessels resulting in a stroke.

Embryological Basis of a Patent Foramen Ovale:
The heart develops from the cardiogenic mesoderm, after the gastrulation phase in the 3rd week of development.

Approximately by day 31, septation of the atria and ventricle begin, ending by week 9, in time for the beginning of the foetal period.

The endocardial cushions emerge from the ventral and dorsal surfaces of the atrioventricular canal, which fuse in the midline, to form the primitive AV septum. Superiorly, in the same plane as the fused cushions, the ‘first septum’ (septum primum) grows towards the fused cushions in an attempt to separate the atria; however due to many perforations in the septum, it ultimately results in a foramen. To make up for this, a second septum (septum secundum) originates adjacent to the septum primum (on the side of the right atria) and develops from the cranial and caudal aspects (unlike septum primum which developed cranio-caudally only). The septum secundum does not fully fuse, which results in the formation of yet another foramen. Simultaneously, the upper part of the septum primum regresses. As a result two foramina exist in tandem, although displaced and not aligned. The caudal part of the first septum (still attached to the fused endocardial cushions) now forms the valve of the foramen ovale.

Source

During intraembryonic life, the valve helps direct most of the mixed blood from the inferior vena cava (which in turn receives mixed blood from the umbilical vein via ductus venosus) into the left atrium, where it flows into systemic circulation for oxygenation. The pulmonary veins at this stage return deoxygenated blood (as the lungs consume oxygen).

After birth, the lungs expand and oxygenate blood, thus increasing the flow of blood towards, and thereby, the pressure in the left atrium. This causes the foramen ovale to close.