56 Anatomy & Embryology with Radiologic Correlates Flashcards
What are the pharyngeal arches?
How are they significant to head and neck development?
What are the pharyngeal arches? How are they significant to head and neck development?
Head and neck formation is intimately related to the development of the pharyngeal arches. Formation of these arches begins at approximately 20 days gestation, and by 28 days four arches are visible. Each arch carries an artery, nerve, cartilaginous bar, and muscle. Of note, the first arch cartilage develops into the maxillary process and mandible. The first arch also carries the mandibular branch of the trigeminal nerve and the muscles of mastication. The second arch carries CN 7 (facial nerve) and the muscles of facial expression.
What primitive structures contribute to the formation of the face?
What primitive structures contribute to the formation of the face?
At the end of the fourth embryonic week, neural crest–derived facial prominences appear from the first pair of pharyngeal arches. Maxillary prominences are found laterally. The frontal nasal prominences develop into the forehead and frontal nasal process. On either side of the frontal nasal prominences are local thickenings that form nasal placodes. These placodes invaginate to form nasal pits and ultimately ridges of tissue that can be divided into a lateral nasal prominence and medial nasal prominences.
Figure: Frontal aspect of the face. A, Five-week embryo. B, Six-week embryo. Illustrated is the relationship of the maxillary promince and the nasal placodes, contributing to the lateral and medial nasal promince.
How and when is the upper lip formed?
How and when is the upper lip formed?
At approximately 6 weeks post conception, the paired maxillary prominences grow medially and contact the paired medial nasal prominences. As fusion of these structures occurs, the upper lip is formed. Ultimately, the maxillary prominences form the lateral lip and the medial nasal prominences form the philtrum, medial upper lip, columella, and nasal tip.
Discuss the embryology of the nose.
Discuss the embryology of the nose.
In the 7-week embryo, five facial prominences contribute to the formation of the nose: the frontal nasal prominence, the paired medial nasal prominences, and the paired lateral nasal prominences. The frontal nasal prominence forms the nasal bridge, the medial nasal prominences fuse and form the nasal tip and columella, and the lateral nasal prominence forms the nasal alae.
How is the primary palate (intermaxillary segment) formed?
How is the primary palate (intermaxillary segment) formed?
Formation of the palate begins concurrently with formation of the upper lip and nose, at the end of the fifth week. In addition to contributing to the nose and upper lip, fusion of the two medial nasal prominences forms the intermaxillary segment. The primary palate includes the hard palate anterior to the incisive foramen.
What is the secondary palate, and how is it formed?
What is the secondary palate, and how is it formed?
The secondary palate refers to the portions of the palate posterior to the incisive foramen. It is formed by the medial migration and midline fusion of the two palatine shelves. These shelves are extensions of the maxillary prominences. Midline fusion proceeds from anterior to posterior, ending with creation the uvula.
Failed fusion of the intermaxillary segment to the maxillary prominences results in what deformity?
Failed fusion of the intermaxillary segment to the maxillary prominences results in what deformity?
Failure of fusion of the intermaxillary segment and maxillary prominence will result in a cleft lip deformity. There is a wide spectrum of cleft lip deformity including a unilateral versus bilateral cleft lip, and a complete versus incomplete cleft lip.
Failure of fusion of the palatal shelves will result in what deformity?
Failure of fusion of the palatal shelves will result in what deformity?
Failed fusion of the palatal shelves, and thus the secondary palate, results in a spectrum of palatal cleft abnormalities. The mildest form of soft palate cleft is a bifid uvula. A submucous cleft occurs when there is midline dehiscence of the palate musculature, but the mucosa remains intact. The most extensive cleft is a bilateral complete cleft of the palate in which the vomer and premaxilla do not fuse with the palatal shelves.
Discuss the embryologic development of the pinna.
Discuss the embryologic development of the pinna.
The pinna develops from the first (mandibular) and second (hyoid) branchial arches. Each arch contributes three hillocks. The first hillock gives rise to the tragus. The second and third hillocks form the crus helicis. The fourth and fifth hillocks become the crura anthelicis and helix, respectively. The sixth hillock forms the antitragus.
Developmental error in hillock formation and/or fusion results in what malformation?
Developmental error in hillock formation and/or fusion results in what malformation?
Microtia is a malformation of the auricle. There can be a wide spectrum of presentation ranging from a small external ear with minimal structural abnormality to an ear with major external, middle, and inner ear structural aberrations.
What are the layers of the forehead and scalp?
What are the layers of the forehead and scalp?
The layers of the forehead are in continuity with layers in the scalp. An effective mnemonic, “SCALP,” describes the five anatomic layers: (S) skin, (C) subcutaneous tissue, (A) galea aponeurosis, (L) loose areolar tissue, and (P) pericranium. The galea aponeurosis is a discrete fibrous layer that is important during both cosmetic and reconstructive procedures. This layer surrounds the entire skull and divides to envelope the frontalis and occipitalis muscles. It is continuous with the temporoparietal fascia (TPF) below the temporal line.
What four muscles are responsible for forehead and eyebrow movement?
What four muscles are responsible for forehead and eyebrow movement?
The frontalis, procerus, paired corrugator supercilii, and paired orbicularis oculi muscles each independently contributes to brow positioning and forehead/glabellar rhytids. It is useful to classify these muscles as brow elevators or brow depressors. The frontalis muscle is the primary and sole elevator of the brow. The procerus, corrugator supercilii, and orbicularis oculi all act as brow depressors.
What is the superficial muscular aponeurotic system (SMAS)?
What is the superficial muscular aponeurotic system (SMAS)?
The SMAS represents a discrete fascial layer that separates the subcutaneous fat from the underlying parotidomasseteric fascia and facial nerve. In the temporal region the SMAS is continuous with the temporal parietal fascia (TPF) and in the neck it is continuous with the platysma. This layer has importance in many procedures in facial plastic surgery such as face lifting (rhytidectomy) and soft tissue reconstruction, and represents an important surgical landmark.
Describe the anatomic structures contributing to the malar prominence.
Describe the anatomic structures contributing to the malar prominence.
The malar prominence is formed by the subcutaneous malar fat pad, which overlies the orbicularis oculi muscle. Deep to this muscle is the suborbicularis orbital fat pad (SOOF). With progressive age, descent of these structures leads to deepening of the nasolabial crease.
What is the relationship of the facial mimetic muscles to the facial nerve?
Why is this anatomic relationship important?
What is the relationship of the facial mimetic muscles to the facial nerve? Why is this anatomic relationship important?
The orbicularis oculi, platysma, and zygomaticus major and minor are considered superficially situated facial mimetic muscles and receive innervation from the facial nerve. These superficially situated muscles receive innervation from the deep surface.
Describe the surface anatomy of the pinna.
Describe the surface anatomy of the pinna.
The surface anatomy of the pinna can be organized into a series of fossae and prominences or ridges, as illustrated in Figure 56-2. The four fossae include the triangular fossa, concha cymba, concha cavum, and scaphoid fossa. The primary prominences include the helix, antihelix, crus, tragus, antitragus, and lobule.
Figure: The surface anatomy of the pinna is described as a series of prominences and depressions.
