Download Where do These Cystic Masses, Fistulae and Sinuses in the Neck

Where Do These Neck Masses, Fistulae and Sinuses Come From?
Yoav Parag M.D., Kalliopi A Petropoulou M.D., Charles R Fitz M.D.
Children’s Hospital of Pittsburgh, University of Pittsburgh Medical Center, Pittsburgh, PA
Introduction
The Clefts
During the 3rd week of gestation the human embryo has
formed the 3 cell lineages (ectoderm, mesoderm and
endoderm) that will form all adult tissues and organs. The
embryo at this stage can be likened to a hollow tube with
a central cavity that represents the primitive gut. The
external surface of the embryonic tube is composed of
ectoderm, the internal surface is composed of endoderm
and there is an intermediary layer of mesodermal cells.
Starting on day 22, six pairs of pharyngeal arches form on
either side of the foregut in the region of the future neck.
These arches are defined externally by ectodermal
infoldings known as the pharyngeal clefts and internally by
invaginations known as the pharyngeal pouches. After
further differentiation 5 arches continue to develop with 5
complimentary pairs of clefts and pouches.
Pharyngeal ( branchia)l arches
1
2
The Pouches
The pharyngeal pouches give rise to important structures in the adult.
The first pharyngeal (branchial) cleft and pouch participate in formation of the ear.
The cleft elongates in a medial direction and the pouch invaginates laterally. These
structures eventually come to lie in close apposition. The first pharyngeal cleft will
become the external auditory canal and the interface with the pouch will become
the tympanic membrane.
Rarely a duplication of the first pharyngeal cleft occurs, resulting in formation of the
first branchial cleft cyst. These cysts are typically located inferior or ventral to the
external acoustic meatus and may become apparent as periauricular swelling.
They may also drain externally through a fistulous tract, usually connecting to the
external auditory canal.
Fig 2a, b : CHCT of the neck reveals a multicystic structure in the left
parotid space (arrows)
Fig 2c,d: Reformatted coronal images show extension of the cyst to the
inferior wall of the left EAC as well as inferior extension to the skin
(arrows). The findings are consistent with first branchial apparatus fistula,
confirmed at surgery
Tongue
The first pouch forms the tubotympanic recess, eventually forming the adult middle
ear structures and the Eustachian tube.
The second pouch gives rise to the palatine tonsils.
1
2
Thyroid
The third pouch splits into a ventral portion that will become the thymus and a dorsal
portion that develops into the inferior parathyroid glands.
The fourth pharyngeal pouch gives rise to the superior parathyroids.
The fifth pouch contains cells that differentiate into the calcitonin producing thyroid C
cells.
Thymus
Figure 9: Coronal section through
the developing neck showing the
migration pathways of the thyroid
from the foramen cecum, the
thymic primordia into the superior
mediastinum and the superior and
inferior parathyroid glands. Notice
the formation of the palatine
tonsils from the second pouch and
the migration of thyroid C cells
from the fifth pouch and into the
center of the thyroid gland
Fig 4a,b,c,d: 14 mo old female presented with right neck mass. CHCT
shows a cystic mass anterior to the sternocleidomastoid muscle
anterolateral to the carotid space and posterior to the submandibular gland.
While this is atypical appearance of a becond branchial cleft byst (a,b), a
track was traced from the inferior aspect of the cyst to the lower neck skin
where a pit was present (arrows)
Figure 6: Schematic representation of the adult neck showing
the typical location of branchial cleft cysts and the typical
draining locations of a cervical sinus.
The other pharyngeal clefts do not form adult structures. During the fourth and fifth
weeks of life the second pharyngeal arch rapidly expands caudally and covers the
other arches and clefts, effectively enclosing the remaining clefts in a transient,
ectoderm-lined cavity called the lateral cervical sinus. In normal development this
cavity disappears, however, if it persists it will become a lateral cervical cyst. If only
one of the clefts persists as opposed to the whole sinus, it will be referred to as a
branchial cleft cyst.
Internal opening
Structures of the third pouch:
By the fifth week of gestation the third pharyngeal pouch splits into a hollow ventral
portion that will give rise to the thymic primordia and a solid dorsal portion that will
give rise to the inferior parathyroid glands.
The thymic primordia elongate inferomedially as thyopharygeal tubes. They detach
from the pouches and migrate to their resting position in the superior mediastinum.
These tubes eventually involute. However, if they do not, thymic rests and cysts will
be seen along the path of migration of the thymic primordia. (Fig 10a, b, c )
The inferior parathyroids detach from the pouches and migrate caudally to the
inferior aspect of the thyroid gland. Any abnormal path of migration will result in
parathyroid ectopia.
The tongue begins to form by the 4th embryonic week from several mesodermal
eminences, arising from the medial aspect of the first pharyngeal arch. At the
intersection of these protuberances, there is a pit called the foramen cecum
where the thyroid primordium develops.
During development the thyroid primordium descends caudally through the soft
tissues of the neck forming a slender thyroglossal duct that eventually detaches
from the foramen cecum and involutes. The thyroid continues to descent until it
comes to lie just inferior to the cricoid cartilage (Fig 11).
Occasionally a portion of the thyroglossal duct persists forming a thyroglossal
duct cyst or a thyroglossal sinus if it communicates with the external surface of
the neck.
Fig 10 a,b,,c,. 9 year old male with a newly found right neck mass. Sagittal and axial FSET2W
sequences reveal cystic masses in both carotid spaces bilaterally (Fig 8a, b arrows). The right
mass extends down to the anterior superior mediastinum (Fig 8c arrow). The association with
the carotid space is suggestive of thymopharyngeal duct cysts, which was confirmed at surgery
Fig 11. 4 year old male
presented with paramedian left
neck mass. CECT shows a cystic
mass imbedded within the left
strap muscle consistent with
thyroglossal duct cyst
3
4
Carotid bifurcation
Pharyngeal ( branchia)l arches
1
1rst Pharyngeal pouch
Fig 5a,b,c,d. 4m0 old male; CHCT demonstrates Second Branchial Cleft
Cyst only on the left but bilateral pits in the lower neck (arrows)
1a
1b
Branchial Arches
Figure 1: Schematic drawing of the embryonic tube at around 4 weeks of gestation (a). The pharyngeal arches are marked by the external
clefts and internal pouches. A coronal section through the embryonic tube (b) shows the mesenchymal core of each arch. Note the central
Figure 7: Schematic illustration of the adult neck in coronal
section, demonstrating a fistulous connection between the
palatine tonsil and the external skin surface through a remnant
cervical sinus cyst.
Fig 10a
2
Fig 10b
Fig 10c
3
prominence at the site of the future tongue primordium.
Take Home Points
4
Clinical presentation may be pits or palpable masses.
The Arches
If a mass lesion is found the images should be scrutinized
for less conspicuous sinuses or fistulae
Figure 3 a and b: Coronal section through the embryonic tube at 6 weeks (a) and 7 weeks (b) of gestation. Notice the overgrowth of
the second pharyngeal arch that covers arches 3 to 5 and the intervening clefts (Fig 2a thick arrow) . Figure 2b (arrow) shows
formation of the cervical sinus, a structure that will be obliterated in normal development
Each arch contains a core of mesenchymal tissue that will give rise to
the future muscles, bones and cartilages of the face and neck. Each
arch is supplied by a solitary artery and innervated by a solitary
nerve. These neurovascular associations continue throughout the
development of the head and neck
Persistent cervical cysts are located just ventral to the sternocleidomastoid muscle.
A completely enclosed cyst may expand to form a palpable lump as its ectodermal
lining desquamates, or becomes infected. Occasionally the cyst communicates
externally through the skin or internally to the pharynx, usually to the embryonic
derivative of the second pharyngeal pouch, the palatine tonsils. Rarely lateral
cervical cysts communicate both internally and externally. These types of fistulae
will be recognized by external drainage of mucous.
References
Benson MT, Dalen K, Mancuso AA. Congenital anomalies of the branchial apparatus: embryology and pathologic anatomy. Radiographics. Sep 1992;12(5):943-60
Brown RL, Azizkhan RG. Pediatric head and neck lesions. Pediatr Clin North Am. Aug 1998;45(4):889-905
Koch BL. Cystic malformations of the neck in children. Pediatr Radiol. May 2005;35(5):463-77
Mukherji SK, Fatterpekar G, Castillo M. Imaging of congenital anomalies of the branchial apparatus. Neuroimaging Clin N Am. Feb 2000;10(1):75-93
Chandler JR, Mitchell B. Branchial cleft cysts, sinuses, and fistulas. Otolaryngol Clin North Am. Feb 1981;14(1):175-86
Fig 8a,b,c,d e, f,g: 24 mo old male presented with right lower neck pit (marked with fiducial). A fistulous track was traced from the pit to the right
palatine tonsil (arrows). At surgery a Second Branchial apparatus fistula was found
Figures 1, 3, 6, 7 and 9 were adapted from KL Morre, TVN Persaud. The Developing Human; Clinically Oriented Embryology 6th Edition 1998 W.B. Saunders