The diaphragma sellae was an important landmark structure in pituitary surgery in the past - extension of a pituitary tumour above it was an indication for a subfrontal approach through a craniotomy. However, a transsphenoidal approach is currently the first preferred option, irrespective of whether there is suprasellar extension.
·
The anterior and
posterior commissures are important neuroradiological landmarks.
Prior to the introduction of modern imaging techniques the anterior and
posterior commissures could be identified by ventriculography.
This led to the use of these two landmarks as the markers of the baseline used
for stereotaxic surgical procedures. This convention is now universal and the
positions of the anterior and posterior commissures are used as the basic
reference points for most surgical atlases of brain anatomy. The narrow
interventricular foramen is located immediately posterior to the column of the
fornix and separates the fornix from the anterior nucleus of the thalamus.
·
The floor of the temporal fossa is formed by the
frontal and parietal bones, the greater wing of the sphenoid, and the squamous
part of the temporal bones. All four bones meet on each side at an H-shaped
junction of sutures termed the pterion.
This is an important landmark on the side of the skull because it overlies both
the anterior branch of the middle meningeal artery
and the lateral (Sylvian) cerebral fissure intracranially (it is also known as
the Sylvian point). The pterion corresponds to the site of the
anterolateral (sphenoidal) fontanelle on the neonatal skull, which disappears
about three months after birth.
·
The
retromandibular vein, formed by the union of the maxillary and
superficial temporal veins (which enter near the points of exit of the
corresponding arteries), is superficial to the
external carotid artery. It is invariably of a reasonable size and is an
important landmark for the facial nerve.
·
Scalenus anterior
forms an important landmark in the root of the neck, because the phrenic nerve passes above it, the subclavian artery
below it, and the brachial plexus lies at its lateral border. The
clavicle, subclavius, sternocleidomastoid and omohyoid, lateral part of the
carotid sheath, transverse cervical, suprascapular and ascending cervical
arteries, subclavian vein, prevertebral fascia and phrenic nerve are all
anterior to scalenus anterior. Posteriorly are the suprapleural membrane,
pleura, roots of the brachial plexus and the subclavian artery: the latter two
separate scalenus anterior from scalenus medius.
·
Posteroinferior
end of the superior turbinate is the most appropriate anatomic
landmark for the identification of the natural ostium
of the sphenoid sinus.
·
The
pterygomandibular raphe - a tendinous band between buccinator and
the superior constrictor - passes downwards and outwards from the hamulus to
the posterior end of the mylohyoid line. When the mouth is opened wide, this
raphe raises a fold of mucosa that marks internally the posterior boundary of
the cheek, and is an important landmark for an inferior
alveolar nerve block.
·
Superior petrosal
triangle as anatomic landmark for subtemporal
middle fossa orientation.
·
Histological studies have shown the radioscapholunate ligament is not a true
ligament because it contains neurovascular
structures which supply the scapholunate interosseous membrane and is
covered by a thick synovial lining. However it a visible landmark inside the
wrist joint when undertaking wrist arthroscopy.
·
A triangular zone ,the triangle of Koch is found between the attachment
of the septal cusp of the tricuspid valve, the anteromedial margin of the
ostium of the coronary sinus, and the round, collagenous, palpable,
subendocardial tendon of Todaro. The triangle is a landmark of particular
surgical importance, indicating the site of the
atrioventricular node and its atrial connections.
·
The pubic
tubercle is an important landmark in distinguishing inguinal from femoral hernias; the neck of the
hernia is superomedial to it in inguinal hernia, but inferolateral in the
femoral form.
·
The main trunk of the inferior mesenteric vein lies either posterior to the duodenojejunal flexure or beneath
the adjacent peritoneal fold. The duodenojejunal flexure is a useful landmark
to locate the vein radiologically or surgically.
·
The ligament of
Treitz is an important landmark in the radiological diagnosis of incomplete rotation and malrotation of the small
intestine.
·
The presacral
fascia provides an important landmark because extension of rectal
tumours through it signifiantly reduces the chance of curative resectional
surgery being possible. Dissection in the plane posterior to it may result in
bleeding from the presacral veins and, since the adventitia of the veins is
partly attached to the posterior surface of the fascia, the haemorrhage may be
severe because the veins are unable to contract down properly.
·
The rectosacral
fascia, or Waldeyer's fascia, is a thick condensation of endopelvic
fascia connecting the presacral fascia to the fascia propria at the level of S4
and extends to the anorectal ring. Waldeyer's fascia is an important surgical
landmark, and its division during dissection from an abdominal approach
provides entry to the deep retrorectal pelvis.
·
The common peroneal
nerve is found emerging posterior to the
biceps femoris tendon, which is thus a useful landmark to find the
nerve and also to avoid injury to the nerve.
·
Flexor hallucis
longus is an important surgical landmark at the ankle: staying lateral to it prevents injury to the neurovascular
bundle.
·
The master knot of
Henry is the anatomical landmark where the tendon of flexor hallucis longus crosses deep to the tendon of flexor
digitorum longus, to reach its medial side in the sole of the foot. The medial plantar nerve can be irritated at the
master knot of Henry: this is usually related to jogging.
·
intersegmental
pulmonary veins form surgical landmarks; thus, a surgeon can remove
a bronchopulmonary segment without seriously disrupting the surrounding lung
tissue and major blood vessels.
·
Sacral cornu or
horn: formed by the pedicles of the fifth sacral vertebra. It is an
important landmark for locating the sacral hiatus.
·
Iliac crests:
a horizontal line connecting the crests passes through the spinous process of
L4 and the intervertebral disc of L4-5; a useful landmark for a lumbar puncture or epidural block
·
Umbilicus:
site that marks the T10 dermatome, lying at the level of the intervertebral
disc between L3 and L4
·
The pectoral
neurovascular bundle is a good landmark in that it indicates the position
of the axillary vein just above and deep (superior
and posterior) to the bundle. This neurovascular bundle needs to be
preserved during standard axillary dissection.
·
The left crus of
the diaphragm is a useful landmark that leads the surgeon to the left inferior phrenic vein.
·
The inferior
epigastric artery and vein are branches of the external iliac
vessels and are important landmarks for laparoscopic
hernia repair.
·
The white line of
Toldt represents the fusion of the mesentery
with the posterior peritoneum. This subtle peritoneal landmark serves
the surgeon as a guide for mobilizing the colon and mesentery from the
retroperitoneum.
·
The mesosigmoid
is frequently attached to the left pelvic sidewall, producing a small recess in
the mesentery known as the intersigmoid fossa.
This mesenteric fold is a surgical landmark for the underlying left ureter.
·
The ureters
lie on the psoas muscle, pass medially to the
sacroiliac joints, and cross the iliac vessels anteriorly. An important
anatomic landmark for easy identification of the ureters is at the site where
the ureters cross anterior to the iliac vessels. After crossing the iliac
vessels, the ureters swing laterally near the ischial spines before passing
medially to penetrate the base of the bladder. In males, the vasa deferentia
pass anterior to the ureters as they exit the internal inguinal ring. In
females, the uterine arteries are closely related to the lower ureters.
·
The three taenia
coli converge at the junction of the cecum with the appendix and can be a useful landmark to identify
the appendix.
·
Descemet's
membrane becomes continuous and uniform, and fuses with the
trabecular beams. The fusion site, known as Schwalbe's
line, is a gonioscopic landmark that defines the end of Descemet's
membrane and the start of the trabecular meshwork.
·
The preaponeurotic
fat pockets in the upper eyelid and the precapsulopalpebral fat
pockets in the lower eyelid are anterior extensions of extraconal orbital fat.
These eyelid fat pockets are surgically important landmarks and help identify a
plane immediately anterior to the major eyelid
retractors.
·
·
The thyrohyoid
membrane pierced by the superior
laryngeal vessels and internal laryngeal
nerves, and Laryngocele (external).
·
The orbital
septum is pierced above by levator palpebrae
superioris and below by the ligament from inferior rectus. The lacrimal,
supratrochlear, infratrochlear and supraorbital nerves and vessels pass through
the septum from the orbit on the way to the face and scalp.
·
The axillary
fascia is pierced by the tail of the
breast.
·
Branches of Musculo
Cutaneous Nerve to biceps and brachialis leave after the
musculocutaneous has pierced coracobrachialis, also
pass between biceps and brachialis, the branch to brachialis also
supplies the elbow joint.
·
The middle meningeal
is the largest of the meningeal arteries. It passes between the roots of the auriculotemporal nerve and may lie
lateral to the tensor veli palatini before entering the cranial cavity through
the foramen spinosum.
·
The buccal branch
of the mandibular nerve passes between the two
heads of lateral pterygoid.
·
The mandibular
part of maxillary artery passes between the neck
of the mandible and the sphenomandibular ligament, parallel with and
slightly below the auriculotemporal nerve.
The pterygopalatine part passes between the two heads of lateral pterygoid to reach the
pterygomaxillary fissure before it passes into the pterygopalatine fossa.
·
The buccal nerve
and maxillary artery passes between the two
heads of lateral pterygoid.
·
The middle
meningeal artery ascends between the sphenomandibular
ligament and lateral pterygoid, passes between the two roots of the auriculotemporal nerve and leaves
the infratemporal fossa through the foramen spinosum to enter the cranial
cavity medial to the midpoint of the zygomatic bone.
·
The mandibular
nerve immediately passes between tensor
veli palatini, which is medial, and lateral pterygoid, which is lateral,
and gives off a meningeal branch and the nerve to medial pterygoid from its
medial side.
·
The auriculotemporal nerve usually has two roots
which encircle the middle meningeal artery. It runs back under lateral
pterygoid on the surface of tensor veli palatini, passes between the
sphenomandibular ligament and the neck of the mandible, and then runs laterally
behind the temporomandibular joint related to the upper part of the parotid
gland.
·
The inferior
alveolar nerve descends behind lateral pterygoid. At the lower
border of the muscle the nerve passes between the sphenomandibular
ligament and the mandibular ramus and enters the mandibular canal via
the mandibular foramen.
·
Sometimes, when the right
subclavian artery is the last aortic branch, it passes between the trachea and oesophagus.
·
GlossoPharyngeal
Nerve curves forwards on stylopharyngeus and either pierces the lower fibres of the superior pharyngeal
constrictor or passes between it and the middle constrictor to be
distributed to the tonsil, the mucosae of the pharynx and postsulcal part of
the tongue, the vallate papillae, and oral mucous glands.
·
The vagus
descends vertically in the neck in the carotid sheath, between the internal
jugular
vein and the internal carotid artery, to the upper border of the
thyroid cartilage, and then passes between the vein
and the common carotid artery to the root of the neck.
·
The pharyngeal branch
of the vagus passes between the external
and internal carotid arteries to the upper border of the middle
pharyngeal constrictor.
·
Lingual Artery
passes between hyoglossus and the middle
constrictor of the pharynx to reach the floor of the mouth accompanied
by the lingual veins and the glossopharyngeal nerve.
·
Stylopharyngeus
is a long slender muscle arises from the medial side of the base of the styloid
process, descends along the side of the pharynx and passes between the superior and middle constrictors to spread out
beneath the mucous membrane.
·
Posterior
interosseous nerve PIN, which passes between the two heads of supinator and enters the extensor
compartment of the forearm.
·
At the elbow the ulnar
nerve is in a groove on the dorsum of the epicondyle. It enters the
forearm between the two heads of flexor carpi
ulnaris superficial to the posterior and oblique parts of the ulnar
collateral ligament.
·
The median nerve
enters the forearm between the two heads of
pronator teres and gives off the anterior interosseous nerve, which
supplies all the flexor muscles of the forearm apart from flexor carpi ulnaris
and the ulnar half of flexor digitorum profundus.
·
The deep palmar
arch and the deep branch of the ulnar nerve pass between the two heads of the adductor pollicis.
·
The superior
thoracic artery runs
anteromedially above the medial border of
pectoralis minor, then passes between it and pectoralis major to gain
the thoracic wall.
·
The femoral nerve
descends through psoas major and emerges low on its lateral border. It passes
between psoas major and iliacus deep to the
iliac fascia and runs posterior to the inguinal ligament into the thigh.
·
The inferior
gluteal passes between the first and second or second and third
sacral anterior spinal nerve rami, then between piriformis
and ischiococcygeus.
·
The profunda
femoris artery passes between pectineus
and adductor longus, then between the latter
and adductor brevis, before it descends between adductor
longus and adductor magnus.
·
The anterior
tibial artery is the terminal branch of the popliteal artery passes
between the heads of tibialis posterior and
through the oval aperture in the proximal part of the interosseous membrane to
reach the extensor region.
·
the mediastinum
is the partition between the lungs and includes the
mediastinal pleura; however, the term is commonly applied to the
region between the two pleural sacs.
·
There are four
anatomical landmarks leading to the identification of the trunk of the facial nerve as it leaves the
stylomastoid foramen.
1. The cartilaginous external auditory meatus
forms a pointer’ at its anterior, inferior border indicating the direction of
the nerve trunk.
2. Just deep to the cartilaginous pointer is a reliable
bony landmark formed by the curve of the bony external meatus and its abutment
with the mastoid process. This forms a palpable groove leading directly
to the stylomastoid foramen. Unfortunately this groove is filled with
fibrofatty lobules that often mimic the trunk of the facial nerve which can lie
as much as 1 cm deep to this landmark.
3. The anterior, superior aspect of the posterior
belly of the digastric muscle is inserted just behind the stylomastoid
foramen.
4. The styloid process itself can be
palpated superficial to the stylomastoid foramen and just superior to it. The
nerve is always lateral to this plane and passes obliquely across the styloid
process. A branch of the postauricular artery is usually encountered just
lateral to the nerve.
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