Author: Rodrigo Arrangoiz MS, MD, FACS, FSSO

• Resistance:
  • Is the impedance of flow:
    • In the tubing and airways and therefore:
      • Can only occur when there is:
        • Airflow
  • According to Ohm’s Law:
    • Resistance (R) = Δ pressure /Δ volume
      • R = (Peak inspiratory pressure – Plateau pressure) / Tidal volume
        • R = (PIP- Pplat) / (TV)
• Assuming a constant tidal volume:
  • The resistance equation can be simplified to:
    • R ≈ (PIP- Pplat)
• Normal airway resistance:
  • Should be ≤ 5 cmH20
• Resistance is a factor in ventilating all patients but can become particularly important:
  • When ventilating patients with COPD or asthma:
    • The resistance in a system:
      • Increases with decreasing diameter
        • While common examples include:
          • A very small endotracheal tube (ETT) or bronchospasm leading to narrowing of the airways:
            • Recall that a “decrease in the diameter” can also occur at just one point:
              • Such as with kinking or biting of the ETT, or a mucous plug in a large airway
• Compliance refers to:
  • The distensibility of the system and is the inverse of elastance:
    • In other words:
      • It a measure of the lung’s ability to stretch and expand:
        • The more elastic a system, or higher the “recoil,”:
          • The lower the compliance:
            • A common analogy to understand the concepts of elastance is to analyze the recoil of springs:
              • Imagine a very tightly wound and stiff spring
              • This spring is difficult to stretch and wants to stay in the coiled position
              • This spring would have high elastance and low compliance
            • Envision a second, loosely coiled spring:
              • Very little force is required to stretch out this spring, and therefore, it has low elastance but high compliance
• Although compliance commonly is used to describe the lung parenchyma:
  • Remember that compliance actually involves all components of the system:
    • In other words:
      • A patient with pulmonary edema may have low compliance:
        • Due to an issue with the lung parenchyma
      • But another patient may have similarly low compliance due to severe chest wall stiffness after a third-degree burn
      • Clinically, knowing the exact cause of decreased compliance in a given patient can be challenging:
        • Physicians should not, therefore, always assume that it is always related to “stiff lungs.”
• In the figure below, the top “lungs” are healthy:
  • The lungs on the left have a resistance problem or impairment in airflow
  • The lungs on the right have a compliance problem or impairment in stretch and recoil
  • In this picture:
    • Both figures could have elevated peak inspiratory pressures (PIP):
      • Due to the excess pressure generated in the system:
        • However:
          • Only the right-hand figure would have an elevate plateau pressure (Pplat):
            • Since this process occurs when there is an absence of airflow

• Compliance (C) = ∆ volume / ∆ pressure
  • C = Tidal volume / Plateau pressure – Peak inspiratory pressure
    • C = (TV) / (Pplat – PEEP)
• Therefore, when troubleshooting high-pressures on the ventilators:
  • Two values are needed:
    • The peak inspiratory pressure (PIP):
      • Is the maximum pressure in the system and includes both:
        • Resistance and compliance:
          • An inspiratory pause stops all airflow:
            • Thereby removing resistance, and only leaving compliance, as illustrated in this diagram below:
              • The plateau pressure, or Pplat, is, therefore:
                • A measure of compliance

• These values can be displayed on the ventilator screen:
  • On most ventilators:
    • The PIP is always seen
    • While the Pplat is seen by pushing the “inspiratory hold” or “inspiratory pause” button on the ventilator
  • An elevated PIP and normal Pplat is:
    • Indicative of increased airway resistance
  • An elevated PIP and elevated Pplat is:
    • Indicative of abnormal compliance

• Determining whether the patient has a:
  • Resistance problem or a compliance problem:
    • Can assist in the differential diagnosis of respiratory failure:
      • High Resistance:
        • High PIP, Low / Normal Pplat:
          • Kinked / obstructed ETT
          • Mucus plugging
          • Brochospasm
          • Endotracheal tube to narrow:
            • Small
          • Coughing
          • Bronchospasm:
            • Obstructive lung disease
  • Low Compliance:
    • High PIP, High Pplat:
      • Atelectasis
      • Pulmonary edema
      • ARDS
      • Hemothorax /pneumothorax
      • Pneumonia
      • Pulmonary fibrosis:
        • Restrictive lung disease
      • Air-trapping with accumulated auto-PEEP
      • Obesity
      • Abdominal compartment syndrome
      • Circumferential burns of the chest
      • Scoliosis
      • Supine position
• Air trapping:
  • Also referred to as breath-stacking:
    • Can lead to the development of auto-PEEP, or intrinsic PEEP (iPEEP):
      • These pressures should be differentiated from the set PEEP, or extrinsic PEEP (ePEEP):
        • ePEEP refers to the additional end-expiratory positive pressure set during mechanical ventilation:
          • To prevent alveolar collapse and derecruitment
    • In contrast:
      • Auto-PEEP, or iPEEP:
        • Is a pathophysiological process:
          • That can occur when the ventilator initiates the next breath prior to complete exhalation:
            • While this is most common in patients with prolonged expiratory phases, such as asthma or COPD:
              • It can also occur in patients:
                • Who have a fast respiratory rate or
                • Those who are being ventilated with large tidal volumes
            • The amount of auto-PEEP can be measured by:
              • Pressing the “expiratory hold” or “expiratory pause” button on the ventilator:
                • When this button is pressed, the ventilator will display the total PEEP:
                  • The auto-PEEP is the difference between the total PEEP and the set PEEP:
                    • Auto-PEEP (iPEEP) = Total PEEP – ePEEP
• The Figure represents the effects of air trapping:

• Air trapping, or autoPEEP:
  • Can lead to significant adverse cardiopulmonary effects
  • The increased intrathoracic pressure from autoPEEP can:
    • Decrease venous return and lead to hemodynamic instability, even cardiac arrest in severe cases
  • The increased pressures may also result in:
    • A pneumothorax or pneumomediastium
  • Additionally, air trapping can lead to:
    • Ineffective ventilation due to:
      • Collapse of the capillaries responsible for gas exchange:
        • With worsening hypercarbia and hypoxemia
    • While this may seem like a paradox:
      • As one may assume that increasing the minute ventilation, or moving more air:
        • Will improve ventilation, there is a limit to the beneficial effects:
          • Once the lungs are overdistended, gas exchange is ineffective
          • In these circumstances, allowing the patient sufficient time to exhale can decrease CO2 retention

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• Prognostic factors:
  • Provide information regarding:
    • Clinical outcome
  • The prognostic factors in breast cancer that have been validated in clinical testing and related to risk of relapse and survival are:
    • Lymph node status
    • Tumor size
    • Grade
    • Lymphovascular invasion
    • ER/PR status:
      • ER-negative and PR-negative tumors:
        • Are associated with a worse prognosis compared to ER-positive tumors
• Predictive factors:
  • Provide information on likelihood of benefit from a given therapy
  • An example of a predictive factor:
    • ER/PR receptor expression:
      • Identifies those patients likeliest to benefit from hormonal therapies
    • Of note:
      • Tumor grade:
        • May be predictive of response to therapy, but not necessarily of survival benefit
• REFERENCES
  • Cianfrocca M, Goldstein LJ. Prognostic and predictive factors in early stage breast cancer. Oncologist. 2004;9(6):606-616.
  • Kleer C, Sabel M. Prognostic and predictive factors in breast cancer. In: Kuerer HM, ed. Breast Surgical Oncology. New York, NY: McGraw Hill; 2010:243-249.

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• #Arrangoiz #BreastSurgeon #CancerSurgeon #BreastCancer

• The NSABP B-35:
  • Is a phase III clinical trial:
    • That randomized postmenopausal women with ER-positive DCIS to:
      • 5 years of anastrozole or tamoxifen:
        • Following breast-conserving surgery and radiation
    • The trial sought to determine:
      • How effective anastrozole is compared to tamoxifen in preventing a breast cancer occurrence:
        • As well as the quality of life of patients taking anastrozole
  • The trial is currently closed after meeting its accrual goal of:
    • 3100 patients
  • Median follow-up of 9 years
  • Investigators found:
    • Significantly fewer breast cancer events in the anastrozole group (n = 90) than in the tamoxifen group (n = 122):
      • Hazard ratio, 0.73; confidence interval, 0.56–0.96, P=0.0234
  • The estimated 10-year breast-cancer-free interval rates were:
    • 93.5% for anastrozole versus
    • 89.2% for tamoxifen
      • This recorded difference in breast cancer-free interval:
        • Was attributable almost entirely to younger postmenopausal women:
          • Less than 60 years of age
  • Interestingly:
    • The difference between treatments did not become apparent until after 5 years of follow-up:
      • Likely due to the low number of events in both groups
  • There was no difference in overall survival (OS):
    • Between the two treatment groups

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• The parapharyngeal space:
  • Also known as the:
    • Prestyloid parapharyngeal space:
      • Is one of the seven deep compartments of the head and neck
• It consists largely of:
  • Fatty areolar tissue
  • Contains branches of the:
    • Trigeminal nerve
  • Deep blood vessels
• Two naming conventions exist in the literature:
  • In the first definition:
    • Familiar to most head and neck surgeons, the parapharyngeal space is divided into:
      • The prestyloid compartment and
      • Poststyloid (retrostyloid) compartment
  • In the second definition:
    • Introduced by some radiologists:
      • The prestyloid parapharygeal space is simply termed:
        • The parapharyngeal space, and
      • The poststyloid pharapharygeal space is termed:
        • The carotid space
• Gross anatomy:
  • The parapharyngeal space:
    • Is shaped like a pyramid:
      • An inverted pyramid with:
        • Its base:
          • At the skull base
        • Its apex:
          • Inferiorly:
            • Pointing to the greater cornu of the hyoid bone
  • Contents:
    • Fat:
      • Main component
    • Deeps blood vessels:
      • Internal maxillary artery
      • Ascending pharyngeal artery
      • Pterygoid venous plexus:
        • Only small portion:
          • Because it is mainly within:
            • The masticator space
    • Nerve:
      • Small branch of the mandibular division of the trigeminal nerve (cranial nerve V):
        • Supplying the tensor veli palatini muscle
    • Salivary glands – depends on the definition:
      • Some say that it contains no salivary glands, others
      • Minor or ectopic salivary gland / rests
      • Retromandibular portion of the deep lobe of parotid gland
    • Lymph nodes
• Boundaries:
  • The parapharyngeal space has complex fascial margins:
    • Occupying the space between the muscles of mastication and the muscles of deglutition:
      • Superior margin:
        • Base of skull
      • Inferior margin:
        • Greater cornu of the hyoid bone:
          • Although some state the space functionally ends higher:
            • With the styloglossus muscle:
              • At the level of the angle of the mandible
      • Medial margin:
        • Middle (pretracheal) layer of the deep cervical fascia:
          • Covering the:
            • Superior pharyngeal constrictor
            • Levator palatini muscle and
            • Tensor veli palatini muscle
      • Lateral margin:
        • Investing fascia (superficial layer) of the deep cervical fascia:
          • Covering the deep lobe of the parotid
      • Anterior margin:
        • Investing fascia (superficial layer) of the deep cervical fascia:
          • Covering the medial pterygoid muscle
      • Posterior margin:
        • Prevertebral layer of the deep cervical fascia
• Relations:
  • Medial:
    • To the masticator space
  • Lateral:
    • To the pharyngeal mucosal space
  • Anterior:
    • To the prevertebral space
  • Posterior:
    • To the medial pterygoid

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• Superficial cervical fascia:
  • Primarily includes the:
    • Platysma and
    • Subcutaneous fat and vessels:
      • However:
        • As with other fascia in the body:
          • The use of the terminology of the superficial cervical fascia has declined in favor of:
            • Subcutaneous tissue:
              • Thus, an unspecified reference to cervical fascia:
                • Mainly refers to the deep cervical fascia
• The deep cervical fascia:
  • Consists of three separate but related fascial layers:
    • That encircle structures in the neck and
    • Allow anatomic compartmentalisation into:
      • The deep spaces of the head and neck
    • Each layer contributes:
      • To the carotid sheath
  • Layers of the deep cervical fascia:
    • Superficial layer of the deep cervical fascia
    • Middle layer of the deep cervical fascia
    • Deep layer of the deep cervical fascia
• The superficial layer of the deep cervical fascia:
  • Also known as:
    • The investing layer / fascia
  • Is the one of three layers of the deep cervical fascia:
    • That surrounds all of the neck:
    • That is deep to the platysma
    • The layer includes:
      • The masticator fascia
      • Submandibular fascia, and
      • Sternocleidomastoid-trapezius fascia
      • The fascia that superficially covers the parotid gland:
        • May also be derived from this layer:
          • But this inclusion is controversial
  • Gross anatomy – attachments:
    • Posteriorly:
      • Ligamentum nuchae
      • Cervical vertebral spinous processes
      • External occipital protuberance
    • Superiorly
      • Mandible:
        • The layer thickens to form the extrinsic ligaments of the mandible:
          • Sphenomandibular ligament and
          • Stylomandibular ligament
      • Mastoid process and styloid process
      • Central skull base
      • Zygomatic arch
      • Superior temporal line or temporal ridge
  • Inferiorly
    • Manubrium
    • Clavicle
    • Acromion and spine of the scapula
  • Contents:
    • The superficial layer of the deep cervical fascia:
      • Encircles everything in the neck:
        • Apart from the skin and superficial cervical fascia (subcutaneous tissue)
    • In addition, it splits to enclose the following structures:
      • Two salivary glands
        • Submandibular gland
        • Parotid glands
      • Two spaces:
        • Masticator space
        • Suprasternal space
      • Two muscles (other than those in the masticator space):
        • Sternocleidomastoid muscle
        • Trapezius muscle
  • In addition:
    • All layers of the deep cervical fascia:
      • Contribute to the carotid sheath
• The middle layer of the deep cervical fascia:
  • Is the one of the three layers of the deep cervical fascia:
    • It most closely surrounds:
      • The visceral organs
  • This layer consists:
    • Anteriorly of the:
      • Strap muscle fascia:
        • Comprised of the:
          • Sterno-omohyoid layer and
          • Sternothyroid layer
          • Thyrohyoid layer
    • Posteriorly:
      • Visceral fascia:
        • Also commonly known as the:
          • Pharyngobasilar and
          • Buccopharyngeal fascia
            • Particularly in the suprahyoid neck, or, less commonly:
              • Pharyngomucosal fascia
        • The alternative term:
          • Pretracheal fascia:
            • May refer to either:
              • The visceral fascia or
              • The sternothyroid-thyrohyoid layer of strap muscle fascia:
                • Which lies anterior to the trachea
  • Gross Anatomy – attachments:
    • Superiorly:
      • Skull base
    • Anteriorly:
      • Hyoid bone
      • Thyroid cartilage
      • Manubrium
    • Inferiorly:
      • Fibrous pericardium
      • Adventitia of the aortic arch
  • Contents:
    • Infrahyoid (strap) muscles:
      • Sternohyoid
      • Omohyoid
      • Sternothyroid
      • Thyrohyoid
    • Visceral space and pharyngeal mucosal space:
      • Buccinator muscle
      • Pharynx and pharyngeal constrictor muscles:
        • Superior pharyngeal constrictor muscle
        • Middle pharyngeal constrictor muscle, and
        • Inferior pharyngeal constrictor muscle
      • Cervical esophagus
      • Thyroid gland* and parathyroid glands
      • Trachea*
      • Larynx*
      • Visceral lymph nodes
      • Recurrent laryngeal nerve
        • *Some sources consider these structures to have their own fascia not derived from the middle layer of the deep cervical fascia:
          • But they are nevertheless considered part of the visceral space
  • In addition:
    • All layers of the deep cervical fascia:
      • Contribute to the carotid sheath:
        • However:
          • In the suprahyoid neck:
            • Above the carotid bifurcation:
              • The contribution of the middle layer is inconsistent
• The deep layer of the deep cervical fascia:
  • Is one of the three layers of the deep cervical fascia:
    • It encases the:
      • Paravertebral muscles and
      • Forms the perivertebral space
    • It consists of the:
      • Perivertebral fascia:
        • The anterior part of which is called:
          • The prevertebral fascia and
          • The alar fascia
  • Gross Anatomy – attachments:
  • Medially:
    • Ligamentum nuchae
    • Cervical vertebral spinous processes and transverse processes
  • Laterally:
    • Carotid sheath
    • First rib:
      • From a portion of the layer called:
        • Sibson fascia
    • Axillary sheath
  • Superiorly
    • The skull base
  • Inferiorly
    • Coccyx:
      • For the prevertebral fascia)
    • Endothoracic fascia:
      • For the alar fascia
  • On each side:
    • A flap attaches to the transverse processes of the cervical vertebrae and:
      • Divides the peri-vertebral spaces into:
        • A pre-vertebral compartment:
          • Anteriorly and
        • A para-spinal compartment:
          • Posteriorly
  • Anteromedial to the scalene muscles:
    • The deep layer splits into two leaves:
      • The ventral leaf being:
        • The alar fascia, and
      • The dorsal leaf being:
        • The prevertebral fascia:
          • With the prevertebral space:
            • Space between the prevertebral fascia and the spine
        • The space between the alar fascia and the prevertebral fascia:
          • Is the danger space
        • The space between the alar fascia and the posterior aspect of the middle layer of the deep cervical fascia:
          • Is the retropharyngeal space
  • Contents:
    • Danger space:
      • Space between prevertebral and alar fascia
    • Prevertebral space:
      • Space between the prevertebral fascia and the spine:
        • Anterior component:
          • Of the perivertebral space
    • Longus colli and capitis muscles
    • Rectus capitis anterior and lateralis muscles
    • Scalenus anterior, medius, and posterior muscles
    • Sheath for subclavian artery and vein, brachial plexus
    • Vertebral column
    • Spinal cord and associated thecal sac, nerve roots, and vessels
    • Vertebrae and associated discs and ligaments
    • Paraspinal / paravertebral space:
      • Posterior component:
        • Of the perivertebral space
    • Levator scapulae
    • Deep cervical back muscles
    • Pierced by the four cutaneous branches of the cervical plexus:
      • Greater auricular nerve
      • Lesser occipital nerve
      • Transverse cervical nerve
      • Supraclavicular nerve
  • In addition:
    • All layers of the deep cervical fascia:
      • Contribute to the carotid sheath

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• The masticator space:
  • Is one of the seven deep compartments of the head and neck
• Gross anatomy:
  • The masticator space are:
    • Paired suprahyoid cervical spaces:
      • On each side of the face
  • Each space is enveloped by:
    • The superficial layer of the deep cervical fascia:
      • The superficial layer of deep cervical fascia:
        • Splits into two at the lower border of the mandible:
          • The inner layer:
            • Running deep to the medial pterygoid muscle and attaches to the skull base medial to foramen ovale and
          • The outer layer:
            • Covering the masseter and temporalis muscles and attaches to the parietal calvaria superiorly
• Contents:
  • Muscles of mastication
  • Ramus and body of mandible
  • Inferior alveolar nerve
  • Inferior alveolar vein and artery
  • Mandibular division of the trigeminal nerve (V3):
    • Enters the masticator space:
      • Via the foramen ovale
  • Pterygoid venous plexus
• Boundaries and relations:
  • Anteriorly:
    • The buccal space
  • Posterolaterally:
    • Parotid space
  • Medially:
    • Parapharyngeal space
• Communications:
  • Masticator space malignancies can spread perineurally:
    • Via the mandibular division of the trigeminal (V3) nerve:
      • Into the middle cranial fossa

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• Maximizing V/Q matching:
  • By preventing atelectasis:
    • Is a key principle in the management of:
      • Respiratory failure
    • Alveolar derecruitment, or atelectasis:
      • Leads to the creation of shunts
    • Atelectasis has multiple detrimental effects in ventilated patients:
      • First:
        • Atelectasis decreases the surface area for gas exchange
      • Atelectasis on a large scale:
        • Is derecruitment
      • Derecruitment is compounded by:
        • Excessive lung weight:
          • Such as with pulmonary edema
        • Chest wall weight:
          • As with morbid obesity
        • Abdominal contents and distention:
          • As with small bowel obstructions)
        • Cardiac compresses:
          • As with pericardial effusion
        • The addition of sedation and paralysis:
          • To positive pressure ventilation:
            • Can further augment this derecruitment
  • This diagram reflects the pressures leading to compression of the lungs when lying a patient supine:
    • The weight of the heart, the weight of the chest wall, the weight of the abdominal contents, and the weight of the lungs themselves

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• Hypoxemia:
  • There are four broad physiologic causes of hypoxemia:
    • Shunting
    • VQ mismatch
    • Alveolar hypoventilation
    • Decreased partial pressure of oxygen
      • Understanding these mechanisms:
        • Allows the clinician at the bedside to quickly develop a differential diagnosis for hypoxemia and target diagnostics to assess for the precise etiology
• Shunts, or blood bypassing normal gas exchange:
  • Is one of the most common causes of hypoxemia
  • A classic example of a shunt is an intracardiac shunt:
    • In this example:
      • Much of the blood passes by the alveoli, participating in normal gas exchange:
        • However, a small amount is diverted through the heart, bypassing the lungs:
          • This deoxygenated blood mixes with the oxygenated blood:
            • Leading to hypoxemia

• When an area of the lung is perfused, but not ventilated:
  • That results in an intra-pulmonary shunt:
    • In other words:
      • The inspired oxygen cannot reach the alveoli for gas exchange
    • There are several different causes of intra-pulmonary shunts, including:
      • Atelectasis
      • Pneumonia
      • Pulmonary edema
      • Acute respiratory distress syndrome (ARDS)
      • Hemothorax
      • Pneumothorax
      • Hyperinflation or auto-PEEPing
        • All of these pathological processes:
          • Prevent effective gas exchange at the alveoli

• When an area has ventilation, but no perfusion:
  • This is dead space:
    • In other words:
      • The airways are functioning normally:
        • But there is a disease process in the vasculature
      • The best example would be a patient in cardiac arrest who is intubated and ventilated:
        • But there is an interruption of chest compressions
    • Dead space can be:
      • Anatomic and physiologic:
        • Such as oxygenation but lack of gas exchange:
          • That occurs in the upper airways, like the trachea
      • There can also be pathological causes of dead space:
        • Such as this diagram of microthrombi blocking a capillary

• Other examples of dead space include:
  • Low cardiac output and hyperinflation:
    • As occurs in obstructive lung disease:
      • In diseases such as chronic obstructive lung disease (COPD):
        • There can be a significant level of hyperinflation or auto-PEEP:
          • Which can lead to vasoconstriction of the capillaries involved in gas exchanged:
            • Thereby leading to impaired gas exchanged
• Dead space ventilation can lead to both:
  • Hypoxia and hypercapnia:
    • Due to CO2 retention

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• The carotid space:
  • Is one of the seven deep compartments of the head and neck
• Gross anatomy:
  • The carotid space is a roughly a cylindrical space:
    • That extends from the skull base through to the aortic arch
  • It is circumscribed by all three layers of:
    • The deep cervical fascia:
      • Forming the carotid sheath:
        • Above the carotid bifurcation:
          • The contribution of the middle layer of cervical fascia:
            • Can be inconsistent and the sheath is interrupted
  • The bifurcation of the common carotid:
    • Usually occurs at the boundary of:
      • The suprahyoid and infrahyoid spaces
• Contents:
  • Common carotid artery:
    • Inferiorly
  • Internal carotid artery:
    • Superiorly
  • Internal jugular vein
  • Ansa cervicalis:
    • Embedded in the anterior wall of the sheath
  • Nerves:
    • Vagus nerve (CN X):
      • Posterior to the vessels:
        • In the posterior notch:
          • Extends below the hyoid to the mediastinum:
            • Within the carotid sheath
    • In the upper part of the carotid sheath, there is also:
      • Glossopharyngeal nerve (CN IX):
        • Anterior to vessels
      • Accessory nerve (CN XI)
      • Hypoglossal nerve (CN XII)
    • Sympathetic nerves:
      • Medial to the vessels and
      • Lateral to retropharyngeal space
  • Deep cervical lymph node chain:
    • Level II, III, IV
• Relations:
  • Suprahyoid carotid space:
    • Superiorly:
      • Masticator space and
      • Para pharyngeal space
    • Laterally:
      • Parotid space
    • Posteriorly:
      • Peri vertebral space
  • The suprahyoid portion of the carotid space:
    • Is often synonymous with:
      • The post-styloid compartment of the parapharyngeal space
  • Infrahyoid carotid space:
    • Anteriorly:
      • Anterior cervical space
    • Laterally:
      • Posterior cervical space
    • Posteriorly:
      • Perivertebral space
    • Medially:
      • Retropharyngeal and visceral space
• Boundaries:
  • Superior margin:
    • Lower border of jugular foramen
  • Inferior margin:
    • Aortic arch
  • Anterolateral margin:
    • Sternocleidomastoid muscle

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