Usmle step 2 secrets pdf

Please forward this error screen to 193. This article is about the human anatomical feature. The skull usmle step 2 secrets pdf birth, showing the anterior and posterior fontanelles.

The skull at birth, showing the lateral fontanelles. The posterior fontanelles ossify within 2 or 3 months after birth. This is called intramembranous ossification. The mesenchymal connective tissue turns into bone tissue. It persists until approximately 18 months after birth. The fetal anterior fontanelle may be palpated until 18 months.

Examination of an infant includes palpating the anterior fontanelle. During birth, fontanelles enable the bony plates of the skull to flex, allowing the child’s head to pass through the birth canal. The sphenoidal and posterior fontanelles close during the first few months of life. The closures eventually form the sutures of the neurocranium. French word fontenele, which is a diminutive of fontaine, meaning “spring”.

It is assumed that the term spring is used because of the analogy of the dent in a rock or earth where a spring arises. Parents may worry that their infant may be more prone to injury at the fontanelles. In fact, although they may colloquially be called “soft-spots”, the membrane covering the fontanelles is extremely tough and difficult to penetrate. Once they are closed, most of the brain is inaccessible to ultrasound imaging, because the bony skull presents an acoustic barrier.

Increased cranial pressure in infants may cause the fontanelles to bulge or the head to begin to enlarge abnormally. In apes the fontanelles fuse soon after birth. In chimpanzees the anterior fontanelle is fully closed by 3 months of age. The problem is often found in conjunction with hydrocephalus, which is a condition in which too much fluid is found within and around the brain, placing pressure on the brain and surrounding tissues. Often the head will appear dome-shaped, and the open fontanelle is noticeable as a “soft spot” on the top of the dog’s head.