Page 325 - Clinical Anatomy

ECA5 7/18/06 6:51 PM Page 310

310 The head and neck

are the sympathetic connections to the eyelid and pupil. The upper thoracic
chain can also be removed via a transthoracic transpleural approach
through the second intercostal space, or by fibre-optic endoscopy. The lung
is allowed to collapse and the chain identified as it lies on the heads of the
upper ribs. Resection of the T2–4 segment results in a warm, dry hand.
2◊◊Horner’s syndrome results from interruption of the sympathetic fibres to
the eyelids and pupil. The pupil is constricted (myosis, due to unopposed
parasympathetic innervation via the oculomotor nerve), there is ptosis
(partial paralysis of levator palpebrae) and the face on the affected side is
dry and flushed (sudomotor and vasoconstrictor denervation). Enophthal-
mos is said to occur, but this is not confirmed by exophthalmometry. The
syndrome may follow spinal cord lesions at the T1 segment (tumour or
syringomyelia), closed, penetrating or operative injuries to the stellate gan-
glion or the cervical sympathetic chain, or pressure on the chain or stellate
ganglion produced by enlarged cervical lymph nodes, an upper mediasti-
nal tumour, a carotid aneurysm or a malignant mass in the neck.

The branchial system and

its derivatives

Six visceral arches form on the lateral aspects of the fetal head separated, on
the outside, by ectodermal branchial clefts and, on the inside, by five endo-
dermal pharyngeal pouches (Fig. 194). In the human embryo the 5th and
6th arches do not appear externally and are represented only by a mesoder-
mal core.
Each arch has its own nerve supply, cartilage, muscle and artery,
although considerable absorption and migration of these derivatives occur
in development. The 5th arch disappears entirely.
The embryological significance of many of the branchial derivatives has
already been discussed under appropriate headings (the development of
the face, tongue, thyroid, parathyroid and aortic arch) but Table 4 serves
conveniently to bring these various facts together.

Branchial cyst and fistula

The second branchial arch grows downwards to cover the remaining
arches, leaving temporarily a space lined with squamous epithelium.
This usually disappears but may persist and distend with cholesterol-
containing fluid to form a branchial cyst. Another theory is that these cysts
arise from squamous clefts in cervical lymph nodes.
If fusion fails to occur distally, a sinus persists at the anterior border of
the origin of the sternocleidomastoid; this branchial fistula can be traced
upward between the internal and external carotids and may even open into
the tonsillar fossa, demonstrating its association with the second branchial
arch.