How to read a Head and Neck CT

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The Basics:

  • Anatomy is the key
  • Follow an organised search routine/check-list

Step 1. Brain and Orbits

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Brain

Search for unexpected findings within the brain:

  • Masses/metastases
  • Hemorrhages
  • Mass effect
  • Aneurysms
  • Etc.

Orbits

Any contributory findings? 

  • Globes
  • Extra-occular muscles
  • Cranial nerves: 2, 3, 4, V1/V2, 6
  • Supraorbital/Infraorbital foramen
  • Conjunctiva
  • Lacrimal glands/ducts 

Step 2. "Special Spaces"

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 "Special Spaces" is a completely made-up term (not for dictations or for the Royal College exam)


There are 2 "Special Spaces" Categories:

1. Connections between the extracranial world and the intracranial world:

  • Superior orbital fissure 
  • Optic canal
  • Foramen ovale
  • Foramen spinosum
  • Foramen lacerum
  • Carotid canal
  • Internal Auditory Canal (IAC)
  • Jugular foramen
  • Hypoglossal canal 
  • Pterygopalatine fossa openings (total of 6): 

                            1. Inferior orbital fissure

                            2. Sphenopalatine foramen

                            3. Pterygomaxillaryfissure

                            4. Foramen rotundum

                            5. Vidian/Pterygoid canal

                            6. Pterygopalatine canal (greater and lesser palatine foramina)  

2. “Hidden” spaces:

  • Pterygomandibularraphe/Retromolartrigone 
  • Buccinatormuscle/buccal space 
  • Inferior alveolar foramen/canal 
  • Mental foramen 
  • Parapharyngeal/Retropharyngeal spaces  

Step 3. Lymph Nodes

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Image: Arch Otolaryngol Head Neck Surg. 1999;125(4):388-396.

First question for you:

  • Known primary tumor: are you expecting to see pathologic lymph nodes?

You see a lymph node that you are concerned about:

  • Does your lymph node have "volume" in all 3 imaging planes?
  • Are the suspicious lymph nodes in the expected drainage pattern fro underlying pathology?

Lymph node morphology:

Homogeneous density:

  • Size--axial plane measures only (don't focus on size):

                        -- 1.0 cm long axis for all, EXCEPT: 

                        -- Level 1B and Jugulodigastric = 1.5 cm

                        -- Retropharyngeal - 0.8 cm

  • Shape/Contour--should have 'volume' in all 3 planes (round, oval)

Heterogeneous density:

  • Necrosis
  • Cystic change 

                        -- Level 2, think HPV+ oropharyngeal SCCa

                        -- Can be present in papillary thyroid carcinoma nodal mets

  • Calcification
  • Extra-nodal extension of tumor (ENE)

                        -- Look for irregular nodal margins 

                        -- Peri-nodal fat must be otherwise clear--no inflammatory change or edema

  • Abnormal contrast enhancement

Hints:

Key to Level 2 = the posterior belly of the digastric muscle (especially when there is no IV contrast)

  • Attaches along the medial aspect of the mastoid tip
  • Courses anteriorly and inferiorly through level 2
  • The lateral margin of the muscle abuts the deep lobe of the parotid gland
  • The medial margin of the muscle abuts the internal jugular vein
  • Jugulodigastric lymph nodes (special Level 2) must touch the posterior belly of the digastric muscle to qualify

Exceptions to the rules:

  • Ipsilateral drainage exceptions: tongue base, lips, midline structures
  • Lateral oral tongue: drainage can be direct levels 3+4, skip 1+2
  • Parotid gland: only major salivary gland with entire complement of lymphatics

Step 4. Mucosal Spaces

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Pharynx:

  • Nasopharynx [A]  
  • Oral Cavity [B]  
  • Oropharynx [C]  
  • Hypopharynx [D]: 

                         --  1. Posterior Wall 

                         --  2. Pyriform Sinus (2) 

                         --  3. Post-cricoid  

                         --  (4.) Posterior confluence of aryepiglottic folds

Larynx:

  • Supraglottic [E] (++ Lymphatics) 
  • Glottic [F] (No Lymphatics) 
  • Subglottic [G] (? Lymphatics)

Step 5. Glands

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Glands

  • Lacrimal
  • Parotid
  • Sublingual
  • Submandibular
  • Thyroid

Step 6. Loose Ends

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Loose Ends:

  • Lungs
  • Bones
  • Skin
  • Vessels
  • Spine