Dr. Mossa-Basha and Dr. Yousem are from the Russell
H. Morgan Department of Radiology, Division of Neuroradiology, Johns
Hopkins University, Baltimore, MD.
Cystic lesions of the
head and neck span congenital, developmental, inflammatory, and vascular
lesions. While these lesions may appear similar on computed tomography
(CT) and magnetic resonance imaging (MRI) scans, their characteristic
locations—midline or laterally, suprahyoid or infrahyoid, deep or
superficial—may suggest a specific diagnosis. Other factors to consider
include the lesions’ fluid density/intensity; whether they are
unilocular or multilocular; whether they are deep or superficial to the
carotid sheath; and whether they are associated with neck organs or with
a specific patient population or syndrome.
This treatise will
take a superior to inferior approach, beginning with skull
base/intracranial lesions (arachnoid cysts), and concluding with
mediastinal (thymopharyngeal), and lateral axillary lesions (lymphatic
cysts are the most common extra-axial intracranial cystic lesions,
representing 1% of all intracranial, space-occupying lesions. The true
incidence of these lesions is unknown, however, as many of them are
asymptomatic.1-5 Arachnoid cysts consist of a cerebrospinal fluid (CSF) collection enveloped by the arachnoid mater in the subarachnoid space.6
Intracranial arachnoid cysts are most commonly found in the middle
cranial fossa (50% to 60%), the parasellar region (10% to 15%), the
quadrigeminal plate cisterns (10%), the cerebellopontine angle (5% to
10%), the supracerebellar cistern (5%), and the cisterna magna (5%).7
Bilateral sylvian fissure arachnoid cysts should raise clinical
suspicion for glutaric aciduria type 1, while posterior fossa arachnoid
cysts are associated with Down syndrome.8,9 Arachnoid cysts
can also be associated with mucopolysaccharidosis, neurofibromatosis
type 1, schizencephaly, Aicardi syndrome, and Landau Kleffner syndrome.8,10 Syndromes associated with each congenital cystic lesion are listed in Table 1.
CT imaging, arachnoid cysts typically appear as unilocular
hypoattenuating lesions (similar to CSF in attenuation) in the
extra-axial space, which can efface the underlying sulci and distort
adjacent brain structures due to mass effect (Figure 1). The lesions can
scallop the overlying bone. On conventional MRI sequences, arachnoid
cysts typically follow CSF signal intensity on all sequences. The
differential diagnosis includes epidermoid cysts, which generally can be
distinguished by their bright signal, indicating reduced apparent
diffusion coefficient on diffusion-weighted images. There can be
underdevelopment of the underlying brain structures secondary to mass
effect, especially those arachnoid cysts affecting the temporal lobe in
the middle cranial fossa.8 Over time, arachnoid cysts can grow, remain stable, or involute.
Rathke’s cleft cysts
cleft cysts are congenital cysts that represent remnants of Rathke’s
pouch, a dorsal invagination of the stomodeal neuroectoderm that ascends
from the oral cavity into the sella to form the adenohypophysis. These
non-neoplastic cysts are found on 11% to 22% of routine autopsies and
are usually asymptomatic.11-13 While most Rathke’s cleft
cysts remain asymptomatic throughout the patient’s life, occasionally
patients can present due to visual symptoms, pituitary dwarfism,
endocrine disturbances, or headaches.14-17
On noncontrast CT imaging, the cysts can be hyperdense, isodense, or hypodense.18 They are rarely suprasellar, but are more commonly intrasellar or both intrasellar and suprasellar.19
Intrasellar lesions are oval shaped, while intrasellar and suprasellar
lesions can be shaped like dumbbells, with a waist at the diaphragm
sella. The most common location of congenital cystic lesions of the head
and neck is listed in Table 2. On MRI, the lesions can vary in T1 and
T2 signal intensities, depending on their proteinaceous content, pure
fluid, and/or blood products (Figure 2). The cysts should have thin,
smooth walls without enhancing mural nodules. Thin cyst-wall enhancement
can be seen (Figure 2), corresponding to chronic inflammatory changes
thought related to foreign body reaction to cyst leakage of mucinous
material. Rathke’s cleft cysts can have areas of enhancement along their
margins, representing displaced and compressed pituitary parenchyma.
T1-hyperintense and T2-hypointense nonenhancing intracystic nodules are
seen in 11% to 77% of cases (Figure 2D).11,19 A phenomenon
known as paradoxical enhancement has been described whereby the
postcontrast cyst intensity may appear lower than the precontrast
intensity.20 The typical imaging appearance of cystic lesions of the neck is described in Table 3.
cephalocele/encephalocele represents a malformation in which
intracranial contents (CSF, meninges, and brain parenchyma) protrude
through a cranial defect. Neurodevelopment in the setting of a
cephalocele, in which brain tissue herniates through the defect, depends
on the size of the lesion, the amount of herniated cerebral tissue, and
associated anomalies. The incidence of encephaloceles is estimated to
be 1 to 4 per 10,000.21-23 The most common types within the
United States (U.S.) and European populations are occipital
encephaloceles; they represent 75% of all encephaloceles amongst the
U.S. population, and are commonly associated with conditions, such as
hemifacial microsomia; Joubert, Chemke, Knobloch, and von Voss
syndromes; and Chiari III, Meckel Gruber and Dandy-Walker malformations.7,24,25
Occipital encephaloceles are frequently associated with abnormalities
of the dural venous sinuses, including absence of the straight sinus and
a persistent falcine sinus.26,27 These lesions can be associated with hydrocephalus or aventriculy.7,24
Occipital encephalocele is typically clinically evident (sincipital).
Imaging studies are ordered to determine whether there are associated
anomalies, and if the dural venous sinuses course into the encephalocele
sac (Figure 3) to avoid surgical resection.
Sincipital encephaloceles, nasal gliomas, dermal sinus tract, and nasal dermoids
(frontonasal, nasoorbital, and nasoethmoidal) encephaloceles, nasal
dermoids, nasal gliomas, and frontoethmoidal sinus tracts all represent a
spectrum of congenital anomalies. They all arise from a lack of
regression of a dural diverticulum in the prenasal space that extends
through the embryologic foramen cecum or the fonticulus frontalis.28
If this dural projection extends to the skin surface, dermal elements
will be pulled in as the diverticulum retracts intracranially, forming a
dermal sinus tract. Dermoid or epidermoid cysts can develop anywhere
along this sinus tract, from the nasal soft tissues to the foramen cecum
adjacent to the crista galli. Sincipital encephaloceles result from
herniation of intracranial contents through the dural projection and
into the nasal cavity. Nasal gliomas (a misnomer as they are not
actually tumors) represent dysplastic heterotopic brain tissue in the
nasal cavity or extranasally in the subcutaneous tissues, which have
embryologically herniated through the dural cleft that later regressed.7
encephaloceles are the most common type of encephalocele in Southeast
Asia, and their occurrence in the U.S. has rapidly increased due to
Asian immigration.29 Frontal encephaloceles, which include
sincipital (outwardly apparent) and basal (not visible externally)
encephaloceles are the second-most common encephalocele, representing
25% of cases.28 Clinical presentation can include CSF leak, rhinorrhea, and meningitis.28,30 Frontal encephaloceles can be associated with frontonasal dysplasia, aberrant tissue band syndrome, and Morning Glory syndrome.25,31
to the evaluation of congenital nasal masses is whether there is
communication or involvement of the intracranial structures.32
MRI is typically the modality of choice, evaluating the lesion as well
as looking for additional intracranial anomalies. On MRI, sincipital
encephalocele will present as a glabellar, prenasal, nasal, or nasal
septum mass, which is continuous with the intracranial contents,
contains CSF signal intensity fluid and brain parenchyma (which may be
T2 hyperintense secondary to gliosis). There can be associated osseous
abnormalities, including widening of the foramen cecum, absence of the
cribiform plate or crista galli with frontoethmoidal encephalocele, or a
defect in the fonticulus frontalis in the setting of frontonasal
encephalocele (figure 4). Nasal gliomas can occur anywhere along the
primitive dural projection, from the nasal soft tissues to the foramen
cecum, similar to dermoid/epidermoid. On MRI, nasal gliomas are
nonenhancing lesions within the nose or anterior to the nasofrontal
suture (actually extranasal) or nasal septum that are T1 isointense and
slightly T2 hyperintense (secondary to gliosis), relative to brain
parenchyma. On MRI, nasal dermal sinus tracts will present as
T1-hypointense linear tract extending from the foramen cecum through the
subcutaneous soft tissues of the midline nasal bridge to the prenasal
space. As stated previously, dermoids or epidermoids can occur anywhere
along this tract, and can even occur intracranially. Epidermoids will
typically follow fluid signal on T1- and T2-weighted sequences, but will
show diffusion restriction, similar to epidermoids elsewhere in the
body. Dermoids will contain areas of T1 shortening and variable T2
signal secondary to intralesional fat.
Sebaceous and epidermal cysts
sebaceous or epidermal inclusion cyst is a common finding in the skin
and subcutaneous tissue in asymptomatic patients. The lesions may be
palpable to the patient and are usually unilocular and ovoid in shape.33
Lipomas may be in the differential diagnosis. On imaging these lesions,
they have cystic density but also variable T1W signal intensity based
on their protein/lipid/keratin content. They have rim enhancement and
are generally bright to mixed intensity on T2W images. Rupture of these
lesions into the skin may induce a local cellulitis, but rarely evolves
into abscesses. Ruptured cysts have a higher rate of septation, thick
and irregular rim enhancement, and spread of abnormal signal and
enhancement into surrounding subcutaneous tissues.
cysts represent benign congenital lesions that arise in the midline of
the nasopharynx, seen in approximately 0.2% to 5% of the population on
MRI studies.34,35 These lesions arise at the contact point between the embryonic notochord and the nasopharyngeal ectoderm.34
There is retraction of nasopharyngeal mucosa with the notocordal ascent
into the clivus. Thornwaldt cysts are typically unilocular and
hypoattenuating on CT. On MRI, they are T2 hyperintense and of variable
T1 signal intensity, depending on proteinaceous content (Figure 5).
There can be thin peripheral cyst-wall enhancement on postcontrast
imaging. Thornwaldt cysts are typically asymptomatic, but they can
result in occipital headaches, persistent nasal discharge, or halitosis
in the setting of infection.36
First branchial cleft cysts
fetal branchial apparatus develops in the 2nd gestational week and
consists of 6 pairs of mesodermal arches separated by 5 ectoderm-lined
branchial clefts externally and 5 endoderm-lined pharyngeal pouches
internally.37 By the 4th week of embryonic life, 4-paired
mesodermal arches are apparent externally, with smaller 5th and 6th
branchial arches not well visualized.38 The 2nd branchial
arch enlarges caudally, extending toward the enlarging epicardial ridge
of the 5th branchial arch. This leads to enclosure of the 2nd, 3rd, and
4th branchial clefts in an ectoderm-lined cavity known as the cervical
sinus of His, which ultimately involutes.39 Branchial anomalies represent 30% of all congenital neck lesions.40
The most commonly discussed branchial apparatus anomalies are cysts,
fistulas and sinus tracts, but they also include thymic cysts, aberrant
parathyroid tissue, and parathyroid cysts.38 The most
commonly accepted theory of anomalous development is persistence of
trapped cell rests from incompletely obliterated branchial apparatus,
resulting in development of branchial cleft cysts later in life. On the
other hand, persistence of a branchial cleft, pouch, or the sinus of His
can produce a branchial sinus or fistula.41 A branchial
sinus represents a tract that communicates externally, and only rarely
internally. A branchial fistula communicates both internally (pharyngeal
mucosa) and externally (neck surface), and relates to persistence of
both a branchial cleft and pouch, while branchial cysts do not
communicate with external or internal surfaces.39 The most common branchial cleft anomalies are cysts, representing 75% of all cases, while 25% are fistulas and sinuses.42
first branchial apparatus normally gives rise to the eustachian tube,
tympanic cavity, mastoid antrum, a portion of the tympanic membrane,
external auditory canal, the mandible, maxilla, and the malleus and
incus.43 For this reason, first branchial cleft cysts, which
represent the second-most common branchial cleft anomaly, can arise
anywhere from the external auditory canal through the parotid gland to
the submandibular triangle. They are associated with branchio-oto-renal
syndrome.44 First branchial cleft cysts most commonly
present with recurrent or refractory abscesses in the periauricular or
parotid region, or at the angle of the mandible. Cysts that communicate
with the external auditory canal can present with otitis, otorrhea
and/or auricular swelling.43 Intraparotid lesions can also
present with parotitis. Complete surgical excision is curative. Arnot
type I cysts are located within the parotid gland without a fistula to
the external auditory canal (Figure 6). Arnot type II cysts are
typically inferior to the parotid gland and may have a fistulous
connection to the ear (Figure 6).
First branchial cleft cysts
appear as simple or complicated unilocular cystic lesions within,
superficial, or deep to the parotid gland on CT and MRI (Figure 7).
Cyst-wall thickness and enhancement varies, depending on whether the
lesion is infected. The imaging appearance is nonspecific and
differential considerations include cystic parotid neoplasms,
lymphadenopathy, sialocele, pseudocyst, retention cyst, or
AIDS-/Sjogren’s-related lymphoepithelial cysts.41
duct obstruction (NLDO) is the most common lacrimal abnormality in
infants and children, occurring in 2% to 30% of newborns, most commonly
secondary to incomplete canalization of the distal nasolacrimal duct,
specifically the valve of Hasner.39,45,46 Dacrocystoceles,
which occur in 0.1% of NLDO cases, represent mucinous distention of the
lacrimal sac, with mucinous material secondary to congenital obstruction
of the nasolacrimal apparatus both proximally and distally.47
There may be marked dilatation of the nasolacrimal duct and lacrimal
sac, which appears as a CSF-intensity lesion on CT and MRI. There can be
thin wall enhancement. When infected, dacrocystocele can appear as a
complicated cyst with preseptal soft-tissue swelling.
are usually benign, but if bilateral, they can rarely result in
stenosis of the nasal aperture, leading to respiratory distress.45
Patients most commonly present shortly after birth with a bluish,
subcutaneous cystic swelling inferior to the medial canthus or a nasal
represent congenital or acquired areas of scleral insufficiency,
secondary to degenerative, traumatic or inflammatory injury, resulting
in focal outward bulging of the globe. Staphylomas are usually lined by
choroidal tissue. These lesions may be isolated findings, or they can be
associated with retinal detachment or severe axial myopia.39
Staphylomas can occur anywhere on the globe, with a focal globe bulge
in a region of uveoscleral thinning. Staphyloma can be associated with
epidermal nevus syndrome and MRCS (microcornea, rod-cone dystrophy,
cataract, and posterior staphyloma).49,50
colobomas are developmental abnormalities resulting from incomplete
closure of the embryonic choroidal fissure. They may affect any part of
the globe, but they favor the optic nerve insertion site.51 These lesions are bilateral in 60% of cases and the globes can be normal-sized or small.52 The most common type involves the inferior temporal aspect of the iris and is not readily seen on imaging.29
There can be involvement of the optic nerve, retina, choroid, iris, or
lens, and when all of these structures are involved, it is known as a
complete coloboma. Coloboma can involve the optic nerve at the optic
disk (Figure 8), with resultant enlargement and excavation of the optic
disk. Microophthalmia with cyst represents a severe malformation in
which a prominent retrobulbar cyst may communicate with the vitreous
cavity, allowing for herniation of vitreous humor through the defect
into the cyst.53 The relative size of the globe and cyst are variable in this setting.
can occur as an isolated congenital abnormality or as part of a
syndromic setting, including CHARGE (Coloboma, Heart malformations,
choanal AtResia, Growth and/or mental retardation, genital anomalies,
Ear anomalies and/or deafness), VATER
(Vertebrae, Anus, Trachea, Esophagus, and Renal), branchio-oculo facial,
Meckel-Gruber, Walker-Warburg, and Goldenhar syndromes; Aicardi, basal
cell nevus; and Trisomy 13 and 18.54,55
Thyroglossal duct cysts
duct cysts (TGDC) represent 70% of all congenital neck masses and are
the most common congenital cervical abnormality after Thornwaldt cysts.56 During the 4th
gestational week, the thyroid primordia, which originates as a
diverticulum in the floor of the primitive pharynx, grows caudally from
the foramen cecum at the junction of the oral tongue and the base of the
tongue, through the prepharyngeal soft tissues along a midline descent,
the anterior neck, anterior and in close proximity to the developing
hyoid bone, to its eventual destination in the inferior neck.40
As the developing gland travels caudally, an epithelial tract is left
behind that develops into the thyroglossal duct, extending from the
foramen cecum, anterior to the hyoid bone, thyrohyoid membrane and
possibly embedded in the strap muscles and to the inferior neck in the
midline.41 The thyroglossal duct frequently forms a recurrent loop behind the hyoid bone.57 For this reason, TGDC can extend through or around the hyoid bone (Figure 9). The duct generally involutes by the 5th to 10th
week of gestation, leaving only a proximal remnant at the foramen
cecum, and a distal portion that differentiates into the pyramidal lobe
of the thyroid gland.40 Persistence of any portion of the
duct can lead to the formation of cysts or ectopic thyroid rests along
the tract. The Sistrunk procedure is performed for removal of TGDC, in
which the cyst, the entire thyroglossal tract, and the central hyoid
bone are removed.
On all imaging modalities, TGDCs appear as
simple unilocular cystic lesions that are most commonly located
juxtahyoid or infrahyoid.58,59 Seventy-five percent of TGDCs occur in the midline, while 25% are within 2 cm of midline in the anterior neck.58
Fifteen percent occur at the level of the hyoid bone, while 60% occur
just inferior to the hyoid, embedded within the strap muscles.43 Thyroglossal duct cysts can have a thin, peripheral, enhancing cyst wall after intravenous contrast administration.
On MRI, intrinsic T1 and T2 signal varies depending on the cyst protein/colloid content, but is usually bright on both.60
Complicated cysts with increased attenuation, internal septations, and a
thick rim of enhancement can result after prior infection or
hemorrhage. A solid enhancing nodule or calcifications within the cyst
should raise suspicion for functioning tissue (1% to 2% of cases) and/or
thyroid carcinoma (most commonly papillary), which arises in < 1% of
all lesions (Figure 10).61 Thyroglossal duct cysts as well as other thyroid anomalies occur in the setting of Cowden syndrome.62
Second branchial cleft cysts
branchial cleft anomalies are the most common branchial apparatus
deformities, representing 95% of all lesions, with cysts being more
common than fistulae and sinuses.63 These lesions are thought
to arise from incomplete obliteration of the embryologic cervical sinus
of His. Second branchial cleft cysts are most commonly found at the
angle of the mandible along the anteromedial border of the
sternocleidomastoid muscle, but can occur anywhere from the
oropharyngeal tonsillar fossa to the supraclavicular neck.64 Second branchial cleft cysts are classified into 4 Bailey types, based on location (Figure 11).65
Type 1 anomalies are anterior to the sternocleidomastoid muscle and
deep to the platysma (Figure 11), while type 2 lesions, which are the
most common type, are found deep to the sternocleidomastoid muscle,
superficial to the carotid sheath (Figures 11 and 12). Type 3 lesions
extend through the carotid bifurcation close to the lateral wall of the
pharynx (Figures 11 and 12). Type 4 lesions are situated adjacent to the
tonsillar fossa, medial to the carotid sheath, where they may present
as parapharyngeal masses (Figure 11). On CT, these lesions are typically
well-circumscribed, homogeneously hypoattenuating, unilocular cystic
lesions, while on MRI, branchial cleft cysts can be T1 hypointense to
intermediate intensity relative to muscle, and are typically T2
hyperintense, similar to CSF intensity, unless traumatized or infected.
Mural thickness, the degree of cyst wall enhancement, complexity of the
lesion, and adjacent soft-tissue edema depend on the extent of
associated inflammation/infection. They are associated with
branchio-oto-renal syndrome and branchio-oculo-facial syndrome.44,66
Metastatic squamous cell lymph nodes can have an appearance similar to
second branchial cleft cysts and should be a consideration in the
appropriate setting. There is a propensity for such cystic lymph nodes
in cases of tonsillar carcinoma and/or HPV-related squamous cell
Dermoids/epidermoids of the floor of the mouth
Dermoids and epidermoids are the second-most common midline cervical anomalies after thyroglossal duct cysts.67
Dermoid and epidermoid lesions are separable by the presence of
epithelial appendages within dermoid cyst walls. Epidermoid cysts are
much less common in the head and neck, and present earlier, usually
during infancy, compared to dermoid cysts.43 Epidermoid cysts
of the head and neck can be associated with Gardner’s syndrome, with
the lesions frequently affecting the scalp, face, and soft tissues of
the neck.68 Dermoid cysts can occur anywhere within the
body, with only 7% occurring in the head and neck, most commonly
involving the lateral brow and nasal regions (as discussed above).43 Approximately 11.5% of dermoid cysts are located in the midline of the floor of the mouth or within the oral tongue.
imaging studies, epidermoid cysts will present as thin-walled cystic
lesions in the submandibular or sublingual space (Figure 13). On CT,
these lesions typically have simple fluid attenuation, with rim
enhancement after intravenous contrast administration. DWI studies show
restricted diffusion, as in intracranial lesions. Alternatively,
dermoids may have fat-fluid and fluid-fluid levels or the lesion may
have a heterogeneous appearance due to the various germinal components.
There may be the appearance of intracystic rounded lesions, relating to
coalescence of fat nodules within the fluid matrix, giving the
appearance of “a sack of marbles.”69 This finding is
virtually pathognomonic for dermoid cysts. MR imaging permits evaluation
of lesion extent in the tongue and floor of the mouth, and the lesion’s
relationship to adjacent muscles. Most dermoid cysts are located
superior to the mylohyoid muscle.40 Dermoid cysts are T1 hyper- to iso-intense, depending on sebaceous lipid content, and are generally T2 hyperintense.
Third branchial cleft cysts
third branchial cleft anomalies are rare, they are still the second
most common congenital lesion of the posterior cervical triangle of the
neck after lymphatic malformations.70 Most third branchial cleft cysts are diagnosed during childhood, and 97% are located on the left side.71
Third and fourth branchial cleft cysts commonly present with recurrent
neck infections (Figure 14). Differentiating third and fourth branchial
cleft cysts from each other can be difficult due to close proximity, but
the relationship of the sinus tract to the superior laryngeal nerve
(derived from the 4th branchial arch) surgically is helpful. Third
branchial cleft anomalies lie superior to the superior laryngeal nerve,
while fourth branchial anomalies lie below. Third branchial cleft cysts
are typically located posterior to the common carotid or internal
carotid artery and sternocleidomastoid (within the posterior cervical
triangle), superior to the hypoglossal nerve, and inferior to the
glossopharyngeal nerve.43 A complete third branchial fistula
has external communication anterior to the sternocleidomastoid muscle.
The tract courses posterior to the common or internal carotid artery,
anterior to the vagus nerve, and pierces the thyrohyoid membrane.38
Traditionally, third branchial cleft anomalies are depicted entering
the base of the pyriform sinus anterior to the fold of the internal
laryngeal nerve; however, Rea et al have described cases in which the
anomaly occasionally originates from the apex of the pyriform sinus.72
branchial cleft cysts most commonly appear on CT and MRI as unilocular
cystic lesions in the posterior cervical triangle. The extent of
cyst-wall thickness and enhancement, cyst complexity and adjacent edema
depends on whether superimposed or previous inflammation/infection
and/or fistulous tracts (which are often superinfected) are present.
There is variable T1-signal intensity depending on the proteinaceous
content, but the lesions are typically T2 hyperintense. Differential
considerations include fourth branchial cleft cysts, cystic/necrotic
lymph nodes, and lymphatic malformations. The definitive treatment is
Fourth branchial cleft cysts
Fourth branchial cleft anomalies are very rare lesions, representing 1% to 4% of all branchial cleft anomalies.73,74
These lesions typically present during early childhood, much like third
branchial cleft anomalies, typically secondary to superimposed, acute,
suppurative thyroiditis, or recurrent abscess formation.75 Fourth branchial cleft anomalies are most commonly sinus tracts and are seen on the left.43
The sinus tract courses from the apex of the pyriform sinus medial and
inferior to the recurrent laryngeal nerve, loops superior to the
hypoglossal nerve, travels along the course of the recurrent laryngeal
nerve within the trachesophageal groove, wraps around the aortic arch on
the left or the subclavian artery on the right. The tract then courses
superiorly dorsal to the common carotid artery, loops around the
hypoglossal nerve and extends medially to the sternocleidomastoid
muscle.76 This depends on the length of the 4th
branchial cleft anomaly, as most do not complete the above mentioned
course. Surgical excision of these lesions with partial thyroidectomy is
the definitive treatment.75
Thymic and thymopharyngeal duct cysts
cysts are very rare cervical masses usually detected during childhood
that can arise within the neck or anterior mediastinum, occurring along
the course of thymic descent. Thymic cysts can occur anywhere from the
angle of the mandible, along the lateral neck, to the sternal notch, but
cervical thymic cysts occur more frequently in the lower third of the
neck on the left side anterior to the sternocleidomastoid muscle.
Overall, these lesions occur much more commonly in the mediastinum than
in the neck (25:1 ratio).77 Nearly half of all cervical
thymic cysts are continuous with the mediastinal thymus, either via
mediastinal extension of the cyst or by a vestigial remnant of thymic
tissue or a solid cord.78 Embryologically, the thymus
originates from the 3rd and 4th pharyngeal pouches. During the 6th week,
as the paired thymic buds develop from ventral outgrowths, the
thymopharyngeal duct forms caudally along the course of migration of the
thymus into the mediastinum.79,80 During the 7th to 10th
week, as the embryologic thyroid migrates into the mediastinum, the
proximal thymopharyngeal duct atrophies and separates from the pharynx.79
Residual thymic tissue or thymic anomalies can arise anywhere along
the thymopharyngeal duct. There are multiple theories regarding the
development of thymic cysts, but 2 of the more commonly held theories
will be discussed here.79 The first believes that thymic
cysts arise from persistence of portions of the thymopharyngeal duct.
The second theory is based upon cystic degeneration of Hassall’s
corpuscles within ectopic thymic tissue within the neck or anterior
mediastinum. Thymic cysts and thymopharyngeal duct cysts are sometimes
used interchangeably, but for our purposes we will use these terms to
refer to a spectrum of disease, with thymopharyngeal duct cyst referring
to a lesion spanning the entire course of the embryologic tract. These
lesions most often present as painless, slowly growing masses in the
lateral neck at the thoracic inlet, close to the thoracic duct insertion
to the subclavian artery.77 Patients can, however, present
with symptoms including upper respiratory infection, coughing,
hoarseness, dysphagia, wheezing, and even respiratory distress secondary
to tracheal compression.81 Thymic cysts usually present
between the ages of 2 and 13 years, later than lymphangioma and earlier
than branchial cleft cysts.79
Preoperative diagnosis of
thymic cysts is difficult, as these lesions are rare and frequently
confused for branchial cleft cysts or lymphangiomas. Cervical thymic
cysts most commonly occur in the lower neck, compared to branchial cleft
cysts that are most often seen in the upper neck.81 Second
branchial cleft cysts usually pass between the external and internal
carotid arteries, while cervical thymic anomalies will pass between the
common carotid artery and the vagus nerve, based on the embryologic
development of the 3rd pharyngeal pouch.78 There
is mediastinal extension in half of cervical thymic cysts while in
contradistinction, only 3% to 10% of lymphangiomas extend into the
mediastinum.81 Lymphangiomas most commonly occur in the
posterior cervical triangle. Thymic cysts are usually unilocular (or
less likely multilocular) elongated cysts, frequently tapered at their
ends, and following fluid signal on CT and MR imaging (Figure 15).78
There can be a thin rim of cyst-wall enhancement on postcontrast
imaging. Complete surgical excision, even with asymptomatic lesions, is
used for diagnosis and treatment. Confirmation of the presence of
mediastinal thymic tissue should be performed prior to removal of thymic
cysts or thymic ectopic tissue to prevent immunocompromise.79
The diagnosis is established by histologic demonstration of residual
thymic tissue and Hassall’s corpuscles in the cyst wall. Congenital
thymic cysts should be differentiated from multilocular thymic cyst, as
the latter represents an acquired, multilocular, inflammatory lesion
arising from cystic dilatation of the medullary duct and having an
association with autoimmune diseases, such as Sjogren’s syndrome and
Lymphatic vascular malformations
vascular malformations are developmental anomalies of the lymphatic
system that can occur anywhere in the body, but 75% affect the head and
neck.40 Lymphangiomas of the head and neck most commonly
occur in the posterior cervical triangle followed by the axilla and the
tongue musculature.83 Lymphangiomas are thought to develop
from sequestration of a portion of the embryologic lymphatics (most
commonly involving the jugular lymph sac), resulting in continued growth
and accumulation of fluid.84 Alternatively, a lymphangioma
may arise from failure of the juguloaxillary lymphatic sac to drain into
the venous system, resulting in obstruction of the lymphatic channel.
Lymphatic vascular malformations are categorized into 3 different
histologic subtypes, determined by the size of the lymphatic channels.
Simple or microcystic lymphangiomas have capillary-sized, thin-walled
lymphatic channels, while cavernous lymphangiomas are composed of
dilated lymphatic spaces and fibrous adventitia. The third type, cystic
hygroma, is a multilocular cystic lesion composed of cysts of varying
sizes.85 All 3 histologic types can occur within the same
lesion. These malformations are commonly detected before the age of 2
years, presenting as slow-growing asymptomatic lesions, but sudden
enlargement can occur in the setting of infection, intralesional
hemorrhage, trauma, or even respiratory tract infection.43
Half are discovered at birth and can present with respiratory compromise
or even death secondary to mass effect on the airway. Hybrid lesions
with venous components are not unusual as low flow vascular
Lymphangiomas of the head and neck most commonly
occur in the posterior cervical triangle, with 3% to 10% extending into
the mediastinum, and 20% involving the axilla.40 The
malformations may also occur in the submandibular space. Lymphangiomas
are frequently transspatial due to their infiltrative nature and do not
respect fascial planes. The size of these lesions is highly variable.
The extent of the lesion is best evaluated on MRI. On MRI, these
multiloculated cystic lesions can have low to intermediate T1 signal,
but occasionally increased T1 signal (Figure 16) secondary to
intralesional hemorrhage, high protein, or fat content. There can be rim
enhancement as well (Figure 16). They uniformly have T2 hyperintensity
unless they have acutely bled. Fluid-fluid levels may be present
secondary to blood. On CT, a lymphangioma can appear as a poorly
circumscribed, homogeneous fluid attenuation mass that may contain
intralesional blood. Infected lesions may contain higher attenuation
fluid. If they are combined with venous vascular malformations, they may
have enhancing solid components. Lymphatic malformations are associated
with fetal alcohol, Turner’s, Down, and Noonan’s syndromes.
Thoracic duct/jugular lymphatic cysts
thoracic duct is the largest lymphatic vessel in the body, draining
lymph and chyle from the subdiaphragmatic body, left arm and chest
(except for the lower lobe of the left lung) into the left
brachiocephalic vein. The thoracic duct arises from the cisterna chyli
in the right abdomen, crosses the diaphragm, and courses cranially just
right of the midline. The duct crosses over to the left at the level of
the 4th vertebral body and passes into the neck, where it forms an arch
just above the clavicle before draining into the left subclavian vein.86
Embryologically, the thoracic duct develops from 6 lymph sacs, with
paired jugular lymph sacs arising at the junction of the internal
jugular veins and subclavian veins.86 Thoracic duct cysts most commonly involve the cisterna chyli, followed by the mediastinum and rarely involve the neck.87
Cervical thoracic duct lymphoceles are rarely congenital, more commonly
arising secondary to thoracic duct injury after neck dissection or
trauma.88 The exact pathophysiologic development of thoracic
duct cysts is incompletely understood. Congenital weakness of the duct
wall or obstruction at the lymphatic-venous junction may contribute to
their development.89 Lymphatic duct wall degeneration
secondary to atherosclerosis, trauma, or infection may also play a
developmental role. Persistence of the fetal jugular lymphatic sac is
thought to result from incompetence or absence of the valve at the
lymphatic-venous junction, thus allowing reflux of blood into the
thoracic duct.88 Thoracic duct cysts typically present with a
painless fluctuant left supraclavicular mass, but they can also present
secondary to mass effect on adjacent structures.
thoracic duct cysts typically occur adjacent to the confluence of the
left subclavian and internal jugular veins in the supraclavicular fossa,
deep to the sternocleidomastoid muscle, and lateral to the carotid
sheath. MRI is optimal for delineating the extent of the lesion and will
show a unilocular or multilocular cystic lesion in the left
supraclavicular fossa with possible retrosternal extension (Figure 17).
Lymphangiography (the gold standard exam) or lymphoscintigraphy can be
performed to confirm communication with the thoracic duct. The diagnosis
is established by fine needle aspiration with return of milky fluid and
biochemical fluid analysis. Asymptomatic lesions can be treated
conservatively, but in the symptomatic setting surgical resection with
thoracic duct ligation or cyst aspiration with sclerosant injection can
cystic lesions of the neck are infrequently encountered disease
processes, which span congenital, developmental, inflammatory, and
vascular lesions. While there may be overlap in cross-sectional imaging
appearances, characteristic locations, cyst fluid attenuation/signal
intensity, association with adjacent structures, and cyst features can
help in differentiating these various lesions. Imaging also allows for
biopsy and surgical planning.
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