Cranial Anatomy Overview

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Questions and Answers

What age does the metopic suture between the two halves of the frontal bone typically disappear?

By 10 years of age

By 5 years of age

By 1 year of age

By 2 years of age (correct)

When does the spheno-occipital synchondrosis typically fuse?

In early adulthood

At 3 years of age

At puberty (correct)

At birth

What is the purpose of cross-sectional imaging such as CT for the skull?

To identify fractures solely

To visualize soft tissue structures

To assess facial bone symmetry

To provide high resolution images of the skull base (correct)

Which fontanelle usually closes by 15-18 months of age?

Anterior fontanelle Signup and view all the answers

Which of the following bones is NOT one of the facial bones that shape the face?

Frontal bone Signup and view all the answers

What is the main purpose of using MRI with narrow section thickness slices?

To demonstrate soft tissue contents of the foramina Signup and view all the answers

What is the consequence of having incomplete metopic sutures in adults?

Mild asymmetry of forehead shape Signup and view all the answers

Which imaging method is preferable to visualize cranial nerves in detail?

MRI Signup and view all the answers

What is located anterior to the tuberculum sellae?

Sulcus chiasmaticus Signup and view all the answers

Which part of the temporal bone is described as pyramidal?

Petrous part Signup and view all the answers

Which cranial fossa is primarily associated with the temporal lobes of the brain?

Middle cranial fossa Signup and view all the answers

What structure lies over the sulcus chiasmaticus?

Optic chiasm Signup and view all the answers

Which structure forms the boundary of the posterior cranial fossa?

Dorsum sellae Signup and view all the answers

What is the primary function of the foramen magnum?

Connects the cranial cavity with the spinal canal Signup and view all the answers

How many projections are typically required for a full assessment of the skull vault?

Several standard projections Signup and view all the answers

Which part of the skull is associated with supporting the frontal lobes of the brain?

Anterior cranial fossa Signup and view all the answers

What is formed by the anastomosis of vessels close to the colon?

Marginal artery of Drummond Signup and view all the answers

Which veins drain the colon corresponding to its arterial supply?

Superior mesenteric veins Signup and view all the answers

What is the anatomical significance of haustra in the proximal colon?

They are fixed anatomical structures. Signup and view all the answers

How does lymphatic drainage occur in the right colon?

To the peripancreatic nodes Signup and view all the answers

In a double-contrast barium-enema examination, which position is best for filling the transverse colon?

Prone position Signup and view all the answers

What percentage of individuals may show faecoliths or fluid levels of the appendix on plain abdominal films?

10% Signup and view all the answers

What is required for the lumen of the appendix to fill during a barium enema examination?

The patient should be supine. Signup and view all the answers

What anatomical feature is observed along the length of the colon?

Taeniae coli Signup and view all the answers

Which part of the large intestine has a maximum diameter of 9 cm?

Caecum Signup and view all the answers

What structure do the taeniae coli converge upon at its proximal and distal ends?

Caecum and rectum Signup and view all the answers

What anatomical structure is present posterior to the first part of the duodenum?

Gastroduodenal artery Signup and view all the answers

What is the average length of the large intestine?

1.5 m Signup and view all the answers

How do appendices epiploicae appear on the large intestine?

Fat-filled peritoneal tags Signup and view all the answers

At which level is the duodenojejunal flexure visible?

L2 Signup and view all the answers

Which colon segment runs from the hepatic flexure to the splenic flexure?

Transverse colon Signup and view all the answers

Which part of the duodenum is indented by the aorta and superior mesenteric vessels?

Third part Signup and view all the answers

What is the average length of the small intestine?

6 m Signup and view all the answers

What variation occurs at the junction of the second and third parts of the duodenum?

It may be redundant and distended with fluid. Signup and view all the answers

Where does the small intestine begin?

Duodenojejunal flexure Signup and view all the answers

Which part of the small intestine is called the jejunum?

First two-fifths Signup and view all the answers

For full angiographic assessment of the duodenum, which arteries must be visualized?

Celiac trunk and superior mesenteric arteries Signup and view all the answers

Study Notes

Sella Turcica

Prominence known as the tuberculum sellae
Groove called the sulcus chiasmaticus, leading to the optic canal
Optic chiasm lies over the sulcus chiasmaticus
Two bony projections on either side of the front of the sella are called the anterior clinoid processes
The posterior part of the sella is called the dorsum sellae, continuous with the clivus
Two posterior projections of the dorsum sellae form the posterior clinoid processes

Temporal Bone

Consists of four parts:
- Squamous part
- Pyramidal petrous part
- Aerated mastoid part
- Styloid process

Zygomatic Process

Projects from the outer side of the squamous temporal bone
Continuous with the zygomatic arch

Occipital Bone

Curved bone that forms part of the skull vault and posterior part of the skull base
Contains the foramen magnum, connecting the cranial cavity with the spinal canal

Cranial Fossae

Anterior cranial fossa
- Limited posteriorly by the sphenoid ridge and anterior clinoid processes
- Supports the frontal lobes of the brain
Middle cranial fossa
- Limited anteriorly by the sphenoid ridge and anterior clinoid processes
- Posterior boundary formed laterally by the petrous ridges and medially by the posterior clinoid processes and dorsum sellae
- Contains the temporal lobes of the brain, the pituitary gland, and most of the foramina of the skull base
Posterior cranial fossa
- Largest and deepest fossa
- Limited anteriorly by the dorsum sellae and the petrous ridge
- Demarcated posteriorly by the groove for the transverse sinus
- Contains the cerebellum posteriorly, pons and medulla anteriorly, which are continuous with the spinal cord through the foramen magnum

Radiographic Projections of the Skull

Standard projections for assessing the skull vault
- Lateral
- OF20 (occipitofrontal view with 20° caudal angulation)
- Towne's
Pituitary fossa visible on:
- OF20
- FO30 (fronto-occipital projection with 30° caudal angulation)
- SMV views
Lateral view is most frequently used for assessing the pituitary fossa

Sutures of the Skull

Metopic suture between the two halves of the frontal bone
- Normally disappears by 2 years of age
- Persists into adulthood in approximately 10% of people
- May be incomplete
Spheno-occipital synchondrosis
- Suture between the anterior part of the occipital bone and the sphenoid body
- Usually fuses at puberty
Intraoccipital or mendosal sutures
- Often seen extending from the lambdoid suture
- Should not be mistaken for fractures
Wormian bones
- Small bony islands seen in suture lines and at sutural junctions, particularly in relation to the lambdoid suture

Cross-Sectional Imaging

Computed tomography (CT)
- Provides excellent visualization of the skull base and foramina with narrow high resolution images
Magnetic resonance imaging (MRI)
- Excellent for demonstrating the soft tissue contents of the foramina, in particular the cranial nerves

Fontanelles

Posterior fontanelle closes by 6-8 months of age
Anterior fontanelle usually closed by 15-18 months
Two pairs of lateral fontanelles close in the second or third month
By 6 months the sutures have narrowed to 3 mm or less

### Facial Bones

Several bones contribute to the bony skeleton of the face, including:
- Mandible, forming the only freely mobile joint of the skull
- Maxillae
- Zygomata
- Mandible
Shape of the face is mostly contributed by the maxillae, zygomata, and mandible
The facial skeleton contains bony cavities:
- Orbits
- Nose
- Paranasal sinuses

### Duodenum

First part of the duodenum passes posteriorly and superiorly
Best air-filled views obtained with the right side raised in a right anterior oblique view
Duodenal cap may be indented by the normal gallbladder
- Thin mucosal folds that are parallel or parallel in spiral, from base to apex
Third part of the duodenum is indented by:
- Aorta posteriorly
- Superior mesenteric vessels anteriorly

### Stomach and Duodenum (CT and MRI)

Junction of the stomach and duodenum marked by increased thickness of the pyloric muscle posterior to the left lobe of the liver
Gastroduodenal artery may be seen posterior to the first part of the duodenum
Second part of the duodenum seen between:
- Liver and gallbladder laterally
- Pancreatic head medially
Third part of the duodenum can always be identified passing between the superior mesenteric vessels and the aorta
Fourth part of the duodenum (duodenojejunal flexure) is visible at the L2 level
Calibre of the duodenum varies according to position and contents
- Junction of second and third part may be redundant and distended with fluid
- Third part may be collapsed and attenuated as it crosses between the aorta and superior mesenteric vessels

Duodenum (Angiography)

For full angiographic assessment, both the coeliac trunk and the superior mesenteric arteries must be visualized

### Small Intestine

Begins where the intestine assumes a mesentery at the duodenojejunal flexure
Ends at the ileocaecal junction
Length varies from 3-10 m, averaging 6 m
Root of its mesentery extends from the left of L2 to the right sacroiliac joint, only 15 cm long
Mobile and lies in mobile coils in the central abdomen
Divided into:
- Jejunum (proximal two-fifths)
- Ileum (distal three-fifths)
- Boundary between jejunum and ileum not well defined

### Appendix (Radiological Features)

Faecoliths or fluid levels of the appendix may be visible on plain films of the abdomen in the right iliac fossa in approximately 10% of individuals
Barium enema
- If the lumen of the appendix is patent, it may fill on barium enema examination
- Lumen is often obliterated in patients past mid-adulthood
- To fill the appendix, the patient should be supine as its orifice is on the posterior aspect of the caecum
- Some elevation of the head is also helpful
CT and MRI
- Normal appendix can usually be identified arising from the caecum inferior to the insertion of the terminal ileum

### Large Intestine

Length is very variable, with an average of 1.5 m
Wider in diameter than the small intestine
- Maximum diameter of the caecum at 9 cm
- Maximum diameter of the transverse colon at 5.5 cm
Marked by taeniae coli (except for the rectum)
- Three flattened bands of longitudinal muscle that represent the longitudinal muscle layer of the colon
- Converge on the appendix proximally and the rectum distally
- Complete longitudinal muscle layer in these structures
- About 30 cm shorter than the colon
- Cause the formation of sacculations along its length, giving rise to the appearance of incomplete septa called haustra on radiographs
Fat-filled peritoneal tags called appendices epiploicae scattered over the free surface of the large intestine, except for the caecum and rectum
- Especially numerous in the sigmoid colon
- Arteries supplying these perforate the muscle wall
Caecum:
- Blind pouch of large bowel proximal to the ileocaecal valve
- Approximately 6 cm long
- Usually has its own mesentery, making it mobile and easily distensible
Ascending colon
- Runs from the ileocaecal valve to the inferior surface of the liver
- Turns medially into the hepatic flexure
Transverse colon
- Runs from the hepatic flexure across the midline to the splenic flexure
Descending colon
- Runs from the splenic flexure inferiorly to the sigmoid colon

### Arteries Supplying the Large Intestine

Each vessel anastomoses with its neighbor forming a marginal artery (of Drummond) close to the colon
Vessels that enter the bowel are, however, end arteries

### Venous Drainage of the Colon

Veins corresponding with the arteries drain to the superior and inferior mesenteric veins

### Lymphatic Drainage of the Colon

Lymph drains to nodes near the bowel wall
These nodes drain to nodes in the mesentery and retroperitoneum along with the mesenteric vessels
Drainage of the right colon to midtransverse colon is with the superior mesenteric vessels to the peripancreatic nodes and superior mesenteric group of para-aortic nodes
Drainage of the left side of transverse and left colon is along the inferior mesenteric vessels to the inferior mesenteric nodes at the origin of the inferior mesenteric artery at the level of the third lumbar vertebra

### Radiological Features of the Colon

Plain films of the abdomen
- Gas within the colon outlines the colon or parts of it
- The sacculation of the colon by the taeniae coli gives rise to septa called haustra
- Haustra are fixed anatomical structures in the proximal colon, but in the distal colon require active contraction for their formation
- Haustra may be absent distal to the midtransverse colon
Double-contrast barium-enema examination
- The entire colon and appendix may be outlined
- Technique for filling the colon with barium and air requires an understanding of anatomy
- Transverse colon, for example, hangs anteriorly between the relatively posteriorly positioned splenic and hepatic flexures, easiest to fill when the patient is prone
- Resumption of a supine position allows filling of the hepatic flexure and the ascending colon with barium
- Junction of the caecum and ascending colon best seen in a prone oblique position

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Description

This quiz covers key structures of the cranial bones, including the sella turcica, temporal bone, zygomatic process, and occipital bone. Test your understanding of the anatomy and functions of these essential parts of the human skull. Ideal for students studying human anatomy or related fields.