Retropharyngeal Region and Pharynx

Atlas References

• Netter: 75, 76, 79, 80, 86–88, 147, 148

• McMinn: 45, 47

• Gray's Atlas: 553–555, 565

Before You Begin

Place the cadaver in the supine position, and identify the following landmarks in the postcraniotomy skull ( Fig. 29.1 ):

• Anterior, middle, and posterior cranial fossae

• Transverse and sigmoid sinuses

• Confluence of sinuses

Dissection Steps

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  With toothed forceps and a scalpel, remove the dura mater from the posterior cranial fossa.

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  With a mallet and chisel, make an inverted V –shaped cut ( dashed line in Fig. 29.2 ) in the posterior cranial fossa ( Plate 29.1 ).

  
  

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  Place the chisel 1 to 2 cm in the front of the foramen magnum at the midportion of the clivus, and make a deep cut.

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  Continue this cut laterally and posteriorly between the jugular foramen and the hypoglossal canal toward the edge of the occipital bone ( Fig. 29.3 ).

  

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  Once the incisions are complete, pull the occipital bone backward to separate it from the skull base.

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  Use a scalpel to cut the soft tissues between the bone fragments.

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  Have a laboratory partner keep the head stable by holding it as shown in Fig. 29.4 .

  

Dissection Tip

Be careful in making the separation in the region posterior to the jugular foramen. This is where the carotid sheath emerges, and aggressive dissection can damage its contents. As you pull the posterior cranial fossa backward ( Fig. 29.5 ), place your finger in the opening you created at the clivus and pull backward ( Fig. 29.6 ).

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  Complete the separation of the posterior cranial fossa and musculature from the retropharyngeal space. Carefully cut any soft tissues obstructing the separation ( Fig. 29.7 ).

  

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  Once the separation is complete, stabilize the head in the upright position, and fully expose the retropharyngeal space ( Fig. 29.8 ).

  

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  Palpate the pharyngeal tubercle , which provides attachment to the fibrous raphe (seam) of the pharynx and is the point of attachment for the superior pharyngeal constrictor muscle ( Fig. 29.9 and Plate 29.2 ).

  
  

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  Identify the sternocleidomastoid muscle laterally.

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  Beneath the tubercle, the buccopharyngeal fascia invests the constrictor muscles of the pharynx.

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  Lateral to this fascia, note a thickened, whitish condensed fascia, the carotid sheath .

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  With forceps, lift up the carotid sheath and expose its contents ( Figs. 29.10 and 29.11 ).

  
  

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  Identify and clean the internal jugular vein, common carotid artery, superior cervical ganglion, and vagus nerve ( Fig. 29.12 ).

  

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  Dissect the internal jugular vein, and identify the accessory nerve at its entrance into the sternocleidomastoid muscle ( Fig. 29.13 ).

  

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  Trace the vagus nerve toward the base of the skull, and identify its inferior (nodose) ganglion and the jugular ganglion. The jugular ganglion of the vagus nerve is located superior to the nodose ganglion.

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  Continue cleaning the carotid sheath and the buccopharyngeal fascia inferiorly ( Fig. 29.14 ), and fully expose its contents ( Fig. 29.15 ).

  
  

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  Identify the superior laryngeal nerve from its origin from the vagus nerve.

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  Trace the hypoglossal nerve from its emergence from the hypoglossal canal ( Fig. 29.16 ). The hypoglossal nerve passes lateral to the internal carotid artery.

  

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  Medial to the internal carotid artery, identify the superior laryngeal nerve . Its internal branch travels near the gap between the middle and inferior constrictor muscles of the pharynx or the space between the external carotid artery and cornua of the hyoid bone.

Dissection Tip

You may encounter multiple lymph nodes around the internal jugular vein. After you identify these, remove them from the field of dissection ( Fig. 29.17 ).

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  Lift the internal carotid artery to trace the pathway of the internal laryngeal artery and its division into internal and external branches (see Fig. 29.17 ).

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  Identify the superior, middle, and inferior pharyngeal constrictor muscles, and carefully clean the buccopharyngeal fascia and adipose tissue (see Fig. 29.17 ).

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  Make a midsagittal incision at the midline of the pharyngeal constrictor muscles to expose the internal aspect of the pharynx and to visualize such structures as the cervical sympathetic trunk and the epiglottis ( Figs. 29.18 and 29.19 ).

  
  

Dissection of Undivided Specimen

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  A different method of dissection of the retropharyngeal space is through the suboccipital region. In this approach, all the musculature of the back, as well as the cervical vertebrae and spinal cord are removed, exposing the retropharyngeal space ( Fig. 29.20 and Plates 29.3 and 29.4 ).

  
  
  

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  The pharyngeal constrictor muscles are especially useful landmarks that can be identified with both dissecting methods as follows:

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    Superior pharyngeal constrictor: Identify the gap between the upper border of the superior pharyngeal constrictor muscle and the base of the skull. Clean the pharyngobasilar fascia that occupies this space, and expose the levator veli palatini muscle, auditory tube, and ascending palatine artery ( Fig. 29.21 ).

    

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    Middle pharyngeal constrictor: This muscle attaches to the greater cornu of the hyoid bone. At the junction of the superior and middle pharyngeal constrictors, identify the stylopharyngeus muscle and the glossopharyngeal nerve (see Fig. 29.21 ).

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    Inferior pharyngeal constrictor: This muscle arises from the sides of the thyroid and cricoid cartilages. At the junction of the middle and inferior pharyngeal constrictors, identify the internal laryngeal nerve and the superior laryngeal artery (see Fig. 29.21 ). The inferior part of the inferior constrictor is also known as the cricopharyngeus muscle.