THYROIDPARATHYROID by zsl11178

VIEWS: 13 PAGES: 52

									THYROID/PARATHYROID
  I. Introduction/General Information
A. Thyroid
    1. Endocrine gland
         a. Lobes are cone shaped
         b. Apex extends to oblique line
             of thyroid cartilage
    2. Highly vascular
    Thyroid, General Information, continued …



3. Anterior & lateral to
      larynx, trachea
4. Lobes connected by
      an isthmus
5. Pyramidal lobe may
      be present
6. Normally not
      palpable
     The Thyroid Gland

   Located in the
    anterior region of
    the neck
   This gland has an
    accessory
    (pyramidal) lobe
     Thyroid Gland, Anterior and Posterior Views




Thyroid Gland: anterior view (left); and posterior view (right)
Thyroid, General Information, continued …




8. Isthmus crosses tracheal
     cartilages 2-4
9. Base located ~4-5th tracheal cartilage
10. Thyroxin function: regulates basic
     metabolism in all cells
Thyroid, General Information, continued


B.    Parathyroid glands

1. Usually four – two on each side
   (2-8 is normal)
2. Lie on the posterior surface of thyroid
3. May be embedded within thyroid gland
4. Regulate calcium/phosphate levels
5. Required for life
  Parathyroid Glands (Post. view of thyroid)




Parathyroid Glands are located on the posterior aspect
  of the thyroid; sometimes the tissue is embedded
  within thyroid tissue.
II. Detailed Anatomy
A. Thyroid
    1. Largest endocrine gland in adult
    2. Normally extends from ~ C-5
       through ~ T-1
    3. Highly vascular
    4. Weights ~20 - 30 grams
Thyroid, Detailed Anatomy, continued …




5. Pyramidal lobe
        a. present in ~ 33% of population.
        b. Extends upward from isthmus
        c. anterior to thyroid cartilage
Thyroid, Detailed Anatomy, continued …




        d. Embryologic remnant of
           thyroglossal duct
        e. formerly connected cecum of
           tongue to thyroid diverticulum
        f. Site of developing gland
Pyramidal Lobe of the Thyroid Gland




    Pyramidal Lobe




                     Thyroid Gland, Anterior View
Thyroid, Detailed Anatomy, continued …




        c. Lobes:
                 1. Attached to cricoid cartilage
                      by ligaments
                 2. Medial surface adapted to
                     larynx and trachea
      Thyroid, Detailed Anatomy, cont …




3. Lobes related posteriorly to the
      esophagus
4. Posterolateral surface
      a. related to carotid sheath
      b. overlaps carotid artery
 Thyroid, Detailed Anatomy, con’t…


d. Isthmus
      1. 1.25 cm x 1.25 cm
      2. Crosses @
      tracheal rings ~2-4
      3. Occasionally
      absent
Thyroid gland vascular, continued …



6. Highly vascular gland supplied by four large arteries
         a. R & L inferior thyroid artery
         b. R & L superior thyroid artery
Thyroid gland vascular, continued …
7. Drained by R & L superior,
   middle and inferior thyroid veins
   a. Veins arise from plexus
    b. on anterior surface of gland
    c. Extend over anterior surface
       of trachea

        Inferior
        Thyroid
           Vein
Thyroid gland, continued …




        d. Lymph vessels
              1. In interlobular connective
                tissue between lobes
              2. Connect with network in wall of
                  gland
              3. terminate in thoracic and
                 right lymphatic ducts
  Thyroid gland, continued …




8. Muscular landmarks
  a. Sternocleidomastoid
     muscles lie laterally
  b. Longus colli (prevertebral)
     muscles lie posteriorly
  c. “Strap” muscles lie
     anteriorly




                                   Strap Muscles
Thyroid gland, continued …




9. Autonomic innervation via
       a. Cervical portion of sympathetic
           trunk
       b. Parasympathetic fibers arise from
           Vagus X
Detailed Anatomy, continued …


9.     Treatment considerations
        a. Superior thyroid artery is
             accompanied by superior
             laryngeal nerve
        b. Inferior thyroid artery is
              accompanied by recurrent
              laryngeal nerve
       Detailed Anatomy, continued …




c. Damaging nerves
results in partial or total
paralysis of larynx
d. Bordered by
neurovascular
structures contained in
carotid sheath
Thyroid gland, continued …


        11. Pretracheal fascia:
                 a. surrounds thyroid
                 b. Extends from hyoid bone to
                      fibrous pericardium
                 c. Encloses trachea, larynx,
                      pharynx, thyroid
                 d. Parathyroids and venous
                      plexus lie between layers
Pretracheal fascia, continued …


        d. Fascia more dense anteriorly
                 1. Thyroid enlargement often
                    occurs posteriorly
                 2. May compress trachea,
                    esophagus
                 3. 1st symptom may be
                    hoarseness, difficulty
                    swallowing
  Parathyroid Gland, Detailed Anatomy

B. Parathyroid glands
 1. Yellow-brown
 2. ovoid or lentiform structures
 3. weigh ~ 50 mg each
 4. Measure 3-10 mm x 2-6 mm x 1-4 mm
Parathyroid Glands, con’t….




        5. Lie between posteromedial
           thyroid lobes and carotid sheath
        6. Close proximity to:
                 a. Tracheoesophageal groove
                 b. longus colli muscles
Parathyroid Glands, continued …




      7. Position of superior glands is more
           predictable
      8. Aberrant glands may lie between
            trachea and thyroid
      9. Blood, lymphatic and nerve supply:
            same as for thyroid
III. Thyroid/Parathyroid Diseases
A.   Ultrasound useful in differentiating
     cystic from complex or solid masses
B.   Thyroid Cysts
     1. Typical cystic appearance
     2. Colloid cysts
     3. Thyroglossal duct cysts
Pathology, cont…


        3. Branchial cleft cysts
                   a. More specific than pattern
                       for other neoplasms
                   b. Are usually more cephalic
        4. Only 20% of thyroid masses are
           simple cysts
Pathology, cont…




C. Structures of Carotid Sheath
    1. Jugular vein, carotid artery
    2. Delineate lateral aspect of thyroid
    3. Jugular vein lateral to carotid artery
          a. vein has greater diameter
          b. Is distensible on valsalva
               maneuver
Transverse Section of Thyroid Gland
                              Trachea

                                        Thyroid Gland, Left Lobe
Sternocleidomastoid Muscle

      Internal Jugular Vein

   Common Carotid Artery



                                                        Brachial Plexus
              Esophagus
Gray-Scale anatomy, continued




D. Thyroid is more homogeneous and
    echogenic than surrounding muscle
        1. Sternocleidomastoid (lateral)
        2. Longus colli (posterior)

E. US is less helpful w/ complex masses
    or diffuse parenchymal disorders
Gray-Scale Anatomy, continued …


F. Parathyroids are difficult to see
        1. Size and location are variable
        2. Usually:
                a. moderately echogenic
                b.   well-circumscribed
                c.   capsule around
                d.   anterior to longus colli
                e.   medial to common carotid a.
Parathyroids, continued …




        3. Longus Colli (“prevertebral”) Muscles
             a. Attachments:
                  1. O = cervical vertebrae
                  2. I = cervical vertebrae
             b. Action: twists, bends neck
             c. Lie posterior
IV. Thyroid Diseases
A. Metastasis from thyroid cancer
    1. May invade local structures
        a. trachea
        b. esophagus
        c. carotid artery
        d. jugular vein
Thyroid Diseases, con’t…


        2. Innervation may be involved
                a. Voice, speech changes
                b. Horner’s Syndrome of eye
                    1. droopy eye
                    2. dryness
                    3. small pupil
  Thyroid Diseases, continued …


B. Cystic Masses
  1. Colloid cyst:
          a. Contains thyroglobulin
          b. May have hemorrhagic center
          c. May be aspirated
Thyroid Follicles showing Colloid



                             Thyroid Follicles
                             with colloid
                             containing Thyroid
                             hormones
Thyroid Diseases, continued …




        2. Branchial cleft cyst
                a. Usually more cephalic
                b. Non-closure of a branchial
                    cleft
                c. lie laterally
Thyroid Diseases, continued …


3. Thyroglossal Duct Cyst
     a. Lies @ midline
     b. Represents non-closure of
             thryoglossal duct
     c. Congenital anomaly:
                1. retention of tract
                2. between thyroid and
                     foramen cecum
Thyroglossal Duct Cyst, Thyroid Disease, continued …




        d. Usually surrounded by hyoid
           bone
        e. More frequently diagnosed in
           pediatric age groups
        f. may be asymptomatic
Thyroid, continued …


        g. Incidence in patients undergoing
             thyroid surgery:
                1. 4%    have this cyst
                2. 28% of those with the cyst
                     are > 50 years old

        h. Symptoms: painless swelling at
            midline of neck
Thyroid, continued …


                i. Treatment:
                         1. excision of cyst & central
                               hyoid bone
                         2. < 1% accompanied by
                               cancer

                j.     Account for ~ 70% of
                         congenital cysts of neck
                k. may appear at any location
                     along duct
  Thyroid Diseases, continued …


C. Complex/Solid Masses (Neoplasm)
  1. Adenoma
          a. Well-encapsulated
          b. Usually solitary
          c. Homogeneous
Thyroid Diseases, Adenomas, continued …


                c. May be complex, with
                        1. sonolucent halo
                        2. echogenic center

                d. 50% of thyroid cancers are
                   papillary adenocarcinomas
        2. Complex  solid masses show
              increased malignancy
Adenoma of the Thyroid Gland

   Note atrophy of the left
    lobe with the tumor
    protruding from it
   Right lobe may
    hypertrohy to
    compensate for loss of
    function in L. lobe
Thyroid, continued …


3. Goiter
        a. Enlargement of thyroid gland
        b. due to insufficient iodine
        c. Gland appears nodular with
           irregular outline
        d. Grossly enlarged
Goiter, continued …




        e. Nodules have variable
           echogenicity
        f. Treatable with iodine in diet
        g. More common inland, and
           before iodized salt
Types of Goiters




 Simple Goiter (L) and Nodular (Toxic) Goiter (R)
D. Parathyroid Diseases
     1. Benign adenoma
         a. Relatively common
         b. usually results in
            hyperparathyroidism
     2. Cancers are rare
     3. Surgical excision gives > 90%
         cure rate
        Parathyroid Diseases

   Pathogenesis of
    Hyperparathyroidism
       PTH increases blood
        calcium levels
       Acts on bone,
        kidneys, small
        intestines
Hyperparathyroidism




    Long-term Effects on the Skeletal System

								
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