What Is the Foramen Ovale?

The oval hole is divided into two types according to the anatomical part, which should be distinguished. One is the oval hole at the base of the skull, which is located on both sides of the saddle. The second is the oval hole of the heart, which refers to a small hole in the left and right atrium septum. Generally speaking, the oval hole refers to the oval hole of the heart.

For radiofrequency temperature-controlled thermocoagulation for trigeminal neuralgia, the accuracy of the oval puncture is directly related to the effect of treatment. Understanding the shape and diameter of the oval hole in the skull base is the key to puncture positioning. There are few reports on the CT appearance of the shape and diameter of the oval hole in Chinese people. The shape and diameter of the oval hole in the CT of the skull base were observed in 205 cases, which are reported as follows.

Human fetal period, a small hole in the left and right atrium septum, left fetal period

Oval foramen is a physiological channel during the embryonic period of the cardiac atrial septum. Around 5 to 7 months after birth, the secondary septum and primary septum of most people's atrial septa adhere to each other and fuse to form a permanent atrial septum. Then oval foramentovale (PFO) is formed. About 25% to 34% of the adult two layers of the oval fossa are not completely fused, leaving a permanent crack-like defect in the middle. Because the partial flow of PFO is too small, it has long been believed that PFO will not cause clinical consequences. In recent years, more and more studies have found that the risk of stroke, migraine, peripheral arterial embolism, and decompression sickness in PFO patients is several times higher than that in normal people. The pathogenic effect of PFO has caused a large number of experts and scholars. Concerned, clinical exploration has adopted closed PFO methods to prevent recurrence of stroke, treat migraine, and recumbent breathing-upright hypoxemia. Although most clinical studies have shown good results, evidence-based studies remain controversial. In order to standardize the clinical application of PFO occlusion, domestic experts in the field, on the basis of drawing on relevant content at home and abroad, combined with China's specific conditions, have formed the "Chinese Experts' Recommendations for the Treatment of Oval Openings", for this work Reference.

PFO Structural characteristics of oval foramen PFO

The structure of the primary septum and secondary septum is different. The primary septum is thin fibrous tissue and has large swings, and the secondary septum is thicker muscular tissue. The degree of overlap between the two compartments is the length of the PFO, and the distance of non-fusion is the width or size of the PFO. The PFO length ranges from 3 to 18 mm, with an average of 8 mm. PFO sizes range from 1 to 19 mm, with an average of 4.9 mm.

According to the diameter of PFO, PFO is usually divided into 3 types: large PFO (4.0mm), medium PFO (2.0 3.9mm) and small PFO (1.9mm). However, in clinical practice, resting esophageal echocardiography Maps (TEE) rarely find large PFOs. PFOs can be divided into simple PFOs and complex PFOs according to their structural characteristics. The characteristics of simple PFOs are: short length (<8mm), no atrial septal tumor (Atrialseptalaneurysm (ASA)), no excessively long Euclidean valve (valvulaEustachii (VE) or Chiari net, non-hypertrophic secondary septum (6mm), and no concurrent atrial septal defect (ASD). Failure to meet the above conditions is a complex PFO.

The function of PFO is similar to that of valves. The normal left atrial pressure is 3 to 5 mmHg (1 mmHg = 0.133kPa) higher than that of the right atrium. The PFO should be closed and generally does not cause blood shunt. Clinical findings suggest that PFO can be associated with left-to-right shunt, right-leftshunt (RLS), or bidirectional shunt. The latter excludes changes in cardiac structural function and increased right ventricular pressure capacity or advanced congenital heart disease with pulmonary hypertension. Seen in transient right atrial pressure higher than left atrial pressure such as end-diastole, beginning of systole, cough, laughter, sneezing, Valsalva action, etc., the weak primary septum on the left side was pushed away and RLS appeared.

PFO Oval foramen PFO and abnormal embolism

Paradoxical embolism refers to thrombosis of the venous system and right atrium from

Figure 3 Suggested treatment options for PFO patients

Embolism caused by right heart entering left heart system. The incidence of abnormal embolism accounts for 2% to 16% of arterial embolism. Clinically, it has been found that cerebral embolism, gas embolism, fat embolism, and neurodecompression sickness during diving are all closely related to abnormal embolism. The necessary conditions for diagnosing abnormal embolism are: RLS mainly present in PFO; the source of the embolism is unknown; diseases caused by abnormal hemodynamics are excluded. However, in patients with clinically suspected abnormal embolism, lower extremity and pelvic vein thrombosis rates are usually not detected, which may be related to imaging detection methods and the difficulty of observing microthrombus. The size of PFO, the amount of RLS and its structural characteristics are closely related to the occurrence of abnormal embolism. The larger the PFO and the more the RLS partial flow, the higher the incidence of abnormal embolism. For PFOs with a diameter of> 4mm, the risk of transient ischemic attack (TIA) and ischemic stroke was significantly increased. PFO combined with ASA, VE and Chiari net is more prone to abnormal embolism. The RESPECT study also confirmed that PFO patients with ASA or a large number of RLS can benefit from occlusion. DeCastro et al. Found that primary atrial septal activity was related to stroke, and PFO-RLS was found to be a high-risk group for stroke occurrence and recurrent stroke when the activity was greater than 6.5 mm.

PFO Diagnosis and treatment process of oval fossa PFO

For patients with clinically confirmed PFO, a treatment plan can be selected according to the process shown in Figure 3. ^[6]