Download salivary gland

imaging of
SALIVARY GLAND
Sangam Kanekar, MD
Assistant Professor
Dept of Radiology and Neurology
Penn State Milton S Hershey Medical Center
Hershey, PA, USA
INTRODUCTION
There are three 3 major, paired salivary glands: the parotid, the submandibular, and the
sublingual glands and multiple (600-1,000) minor salivary glands which line the mouth,
palate, lip and rarely found in the nose.
Embryology:
The major salivary glands develop from the 6th-8th weeks of gestation from the buds
from the epithelial lining of the mouth. The parotid develops first, and grow
surrounding the VIIth nerve but it is the last to become encapsulated (after the
lymphatics develop), resulting in entrapment of lymphatics in the parenchyma of the
gland. A mesh of unique glandular stroma consisting of epithelial cells, myoepithelial
cells, adipocytes, lymphatic channels, and lymph nodes.
Note: The other major salivary glands do NOT have intraparenchymal lymph nodes.
The minor salivary glands develop after the major salivary glands and arise from oral
ectoderm and nasopharyngeal endoderm.
PAROTID GLAND
ANATOMY
The paired parotid glands (para=around & otid=ear) are the largest of the major salivary
glands located in the preauricular region. The deep cervical fascia continues superiorly
to form the parotid fascia, which is split into superficial and deep layers to enclose the
parotid gland. The thicker superficial fascia is extended superiorly from the masseter
and sternocleidomastoid muscles to the zygomatic arch. The deep layer extends to the
stylomandibular ligament, which separates the superficial and deep lobes of the parotid
gland.
Superficial layer of the
deep cervical fascia
Retromandibular
vein
PAROTID GLAND
ANATOMY
Stylomandibular canal
deep lobe
Superficial lobe
deep lobe
Gland is divided by the facial nerve into a superficial & deep lobe. The superficial
lobe, is lateral to the facial nerve while deep lobe is medial and lies within the
parapharyngeal space. Most benign neoplasm are found within the superficial lobe &
can be treated with superficial parotidectomy. Tumors arising in the deep lobe of the
parotid gland requires wider excision. The parotid gland is bounded superiorly by the
zygomatic arch. Inferiorly, the tail of the parotid gland extends down and abuts the
anteromedial margin of the sternocleidomastoid muscle. This tail of the parotid gland
extends posteriorly over the superior border of the sternocleidomastoid muscle toward
the mastoid tip.
PAROTID GLAND
ANATOMY
buccinator muscle
parotid duct
Accessory parotid glands tumor
Stensen’s duct (parotid duct) arises from the anterior border of the parotid and parallels
the zygomatic arch. Duct runs superficial to the masseter
muscle, then turns sharply
medially to pierce the buccinator muscle at the level of the second maxillary molar
where it opens onto the oral cavity.
Accessory parotid glands
are found in approximately 20% of the population and lie
over the massester muscle. Histologically they are identical to normal parotid gland
tissue. Accessory parotid tissue is susceptible to most salivary pathologies. Between 17% of all parotid neoplasms arise from accessory glands, 50% of which are malignant.
SUBMANDIBULAR GLAND
ANATOMY
The Submandibular gland (SMG) is the second largest salivary gland and lies in the
submandibular triangle formed by the anterior and posterior bellies of the digastric
muscle and the inferior margin of the mandible. Besides SMG, lymph nodes, facial
artery and vein, mylohyoid muscle, and the lingual, hypoglossal, and mylohyoid nerves
also lie within the triangle. The middle layer of the deep cervical fascia encloses the
submandibular gland. The Submandibular duct (Wharton’s duct) exits the medial
surface of the gland and runs between the mylohyoid (lateral) and hyoglossus muscles
and on to the genioglossus muscle.
SUBLINGUAL GLAND
ANATOMY
SLG is almond shape and is the smallest of the major salivary glands. It lies just deep
to the floor of mouth mucosa between the mandible and Genioglossus muscle and
bounded inferiorly by the Mylohyoid muscle. Unlike the Parotid and SMG, the SLG
has no true fascial capsule. Gland lacks a single dominant duct, instead, it is drained by
approximately 10 small ducts (the Ducts of Rivinus), which either secrete directly into the
floor of mouth, or empty into Bartholin’s duct that then continues into Wharton’s duct.
SL & SM SPACES
ANATOMY
Fig SLS and SMS anatomy. Mylohyoid muscle (yellow arrow), Submandibular gland in submandibular
space (green arrow), sublingual space (red arrow).
SUBLINGUAL SPACE (SLS): is inferomedial to the myelohyoid muscle in the oral
cavity. There is no true fascial lining of SLS. No fascia separates the posterior SLS
from SMS as the result lesions of the SLS readily spread to the SMS.
SUBMANDIBULAR SPACE (SMS) is located inferolateral to the mylohyoid muscle
and superior to the hyoid bone. The superficial layer of deep cervical fascia split to
encircle the SMS. SMS is a horseshoe shape space found between the hyoid bone
below and the mylohyoid muscles sling above. Posteriorly, SMS runs into
parapharyngeal space and posterior portion of SLS.
HYPOPLASIA of GLAND
absence of left SMG
absence of left parotid gland
Hypoplasia or absence of the major salivary glands with or without the absence of Stensen’s
duct has been documented and may be partial or total. It is not usually associated with accessory
or ectopic salivary tissue. Familial absence of these glands have also been documented. Lacrimal
apparatus malformations (agenesis, aplasia) may be associated, this combination is known as
lacrimo-auriclo-dentodigital (LADD). Total parotid agenesis may lead to reduction in salivary
flow and may lead to dental caries and infection. Note: The submandibular, sublingual and minor
salivary glands contribute most significantly to the total resting salivary flow. Therefore
unilateral or partial parotid agenesis may not be noticed by the patient.
IMAGING OF THE SALIVARY GLANDS
CT, MR, and ultrasound are the imaging modalities of choice with respect to the
salivary glands.
General rule: CECT for inflammatory diseases and MR for the evaluation of tumors.
Ultrasound is very useful for inflammatory or superficial disease.
Sialograms (rarely performed today) used to be the mainstay of major salivary gland
imaging, and they remain the most detailed way to image the ductal system.
Healthy parotid gland is fatty with numerous thin strand-like structures interlacing
through it. In children and some adults, a clinically normal parotid can have less fat
content, making it difficult to distinguish healthy from diseased parotid.
Normally, the facial nerve is NOT imaged.
USG
CT
MR
LESIONS
NON-NEOPLASTIC
Infective
Sialolithiasis
Acute
Bacterial
Viral
Chronic
TB
Sarcoid
NEOPLASTIC
Trauma
RT
Autoimmune
Sialosis
Cystic lesions
Hyperlipidemia
Congenital
Acquired
Vascular
Hemangiomas
infantile hemangioma,
rapidly involuting congenital hemangioma
(RICH),
non-involuting congenital hemangioma
(NICH).
Vascular malformations
Venous
Capillary (port-wine stains)
Lymphatic (cystic hygromas)
Arteriovenous
Mixed
Venous-lymphatic
Venous venular
INFECTION
Bacterial infection
Fig Bacterial sialadenitis. CECT, axial and coronal images show
diffusely enlarged left SM gland with diffuse inflammation in the SM
space and enhancement of the duct.
Bacterial infection: Most of this infection ascend from the oral cavity related to the
decrease in the salivary flow due to various reasons (trauma, surgery, radiation).
Ascending infections are more common in parotid than SMG because: Stenson’s duct
orifice is larger then Whartson’s, SMG secretions are mucinous and are bacteriostatic.
Eosinophic mucus plug or food, seed particles are seen at the orifice. Most common
organism is S.Aureus followed by S.viridans, H. influenzae and E. colli.
INFECTION
Bacterial infection
Fig: CECT: axial & coronal images show large Fig: coronal and sagittal CT reformatted images
abscess.
show enlarged SMG with abscess in the lateral
aspect of the gland.
In severe infections liquefactions have to be excluded, especially in diabetic and HIV patients.
SMG abscess are more common than parotid due to obstructive stone in SMG. S. Aureus are the
commonest type of pathogen and are responsible 40% of abscess. In gray-scale sonography
meticulous investigations are necessary in order to visualize moving debris in an abscess. CT
may show enlarged gland with hypodense collection which may show peripheral enhancement.
An abscess can be drained under US guidance
INFECTION
Viral infection
Fig: Left viral parotitis: Left parotid is inflammed and
enlarged and shows mild enhancement on post
contrast.
Fig: Bilateral viral parotitis: CECT shows bilateral
enlargemnt of gland and moderate enhancement.
Clinically glands were painful bilaterally.
The most common cause of viral parotitis is mumps by RNA virus. It mainly involves
the parotid gland and rarely SM or SL glands. The disease is characterized by acute
painful swelling of the involved gland. Saliva is infective during the acute phase.
Imaging findings are non-specific. The gland is usually enlarged and has a slight greater
CT attenuation than normal. On MR gland tends to have a slight higher signal intensity
then normal.
HIV Sialopathy
Fig: Lymphoepithelial cyst in HIV patient.
INFECTION
Fig: Uunilateral lymphoepithelial cyst in HIV patient.
Parotid enlargement is seen in around 5% of HIV positive patients and most of these are due to
BLEL. BLEL are frequently multiple; bilateral or unilateral; cystic, partial cystic, or solid. The
cystic lesions are not entirely simple and contain internal echoes and septations. Occasionally,
HIV causes a large solitary unilateral cyst with internal echoes. The lack of internal color Doppler
flow and FNA confirm the cystic nature of these lesions. The CT and MR features of BELL are
nonspecific. Solid BHEL cannot be radiologically differentiated from benign or malignant
tumors. Partially cystic lesions mimic Warthin’s tumor.