In anatomy, a persistent left superior vena cava is the most common variation of the thoracic venous system. It is present in between 0.3% and 0.5% of the population, and is an embryologic remnant that results from a failure to involute. Presentation
In persistent left superior vena cava, the left brachiocephalic vein does not develop fully and the left upper limb and head and neck drain into the right atrium via the coronary sinus.In isolation, the variation is considered benign, but is very frequently associated with cardiac abnormalities (e.g. ventricular septal defect, atrioventricular septal defect) that have a significant mortality and morbidity. It is more frequent in patients with congenital heart defects.The (right) superior vena cava is almost always unaffected by the presence of persistent left superior vena cava. Diagnosis
If an anomaly is detected during a routine ultrasound, a fetal echocardiogram is performed to determine whether a fetus has the condition. Otherwise, it is often unnoticed unless an extenuating circumstance warrants further examination of the heart, usually much later in life.CT and MRI scans in a parasagittal section may show a "pipe" sign where the left superior vena cava occurs. Treatment
If no other cardiac abnormalities are present, persistent left superior vena cava will not be treated, as it is usually asymptomatic and unharmful. If it drains into the left atrium, then deoxygenated blood enters the circulation to the body, and cyanosis may occur. References


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The most commonly involved tooth in localized microdontia is the maxillary lateral incisor, which may also be shaped like an inverted cone (a "peg lateral"). Peg laterals typically occur on both sides, and have short roots. Inheritance may be involved, and the frequency of microdontia in the upper laterals is just under 1%. The second most commonly involved tooth is the maxillary third molars, and after this supernumerary teeth. Causes
There are many potential factors involved. Congenital hypopituitarism
Ectodermal dysplasia
Down syndrome
Ionizing radiation to the jaws during tooth development (odontogenesis)
Chemotherapy during tooth development
Marshall syndrome
Rieger syndrome
Focal dermal hypoplasia
Silver-Russell syndrome
Williams syndrome
Gorlin-Chaudhry-Moss syndrome
Coffin–Siris syndrome
Salamon syndrome
Cleft lip and palateOthers include trichorhinopharyngeal, odontotrichomelic, neuroectodermal and dermo-odontodysplasia syndromes. Treatment
Unerupted microdonts may require surgical removal to prevent the formation of cysts. Erupted microdonts, peg laterals especially, may cause cosmetic concern. Such teeth may be restored to resemble normal sized teeth, typically with composite build ups or crowns. Orthodontics may be required in severe cases to close gaps between the teeth. Epidemiology
Females are affected more than males, and the condition occurs in permanent (adult) teeth more than deciduous (baby teeth or milk teeth). References


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