BRANCHIAL CYSTS : A CASE REPORT OF A BENIGN LYMPHOEPITHELIAL CYST IN THE NECK WITH REVIEW OF LITERATURE
Pranava Sinha, Shivkumar S Utture
*Surgical Registrar; **Honorary Associate Professor, Dept. of General Surgery, Grant Medical College, Sir JJ Group of Hospitals, Mumbai.
Branchial cysts or lymphoepithelial cysts have been known to occur in neck anterior to the upper third of the sternomastoid. Although they have been reported to occur in the other regions of the anterior triangle of the neck, a cyst in the posterior triangle of the neck is extremely rare. This is a report of such a case with review of the available literature.
Branchial cysts are the commonest cysts to arise in the neck. In the early descriptions they were described as to arise anterior to the sternocleidomastoid muscle. However there have been a number of case reports describing cysts which were found in areas other than the classical position. Just as there have been various sites for the cysts, there have been a number of theories proposed as possible aetiologies. This is a case report of a branchial cyst found in the posterior triangle of the neck with a review of the available literature.
A 23 year old female presented with a solitary swelling in the left side of the neck of 6 months duration. Initially the swelling was of the size of pea, and gradually increased with time to attain the size approximately equal to the size of the patient’s fist. There was no pain in the swelling. On examination an 8 cm x 7 cm swelling was found in the left posterior triangle of the neck. It extended from the anterior border of the left sternomastoid to the anterior border of the left trapezius, anteroposteriorly and from the level of the thyroid prominence superiorly to about 3 cm medial to acromion process inferiorly. The smooth, well-defined swelling was fluctuant and brilliantly transluminant. On operation a well-circumscribed unilocular cyst was found without any connecting tract or cord to the skin or the pharynx. The cyst contained clear yellowish fluid. Microscopic examination of the cyst wall revealed a focally preserved flattened cuboidal epithelial lining with lymphocyte aggregates in the underlying collagenous wall.
REVIEW OF LITERATURE
Lateral cysts of the neck were first described by Hunczovsky in 1785.  Since then these swellings have been described by various names and various aetiological hypotheses have been proposed for them.
These hypotheses can be conveniently classified as the "Congenital theories" and the "Lymph node theories". Rathke described pharyngeal pouches in 1828. Following this Ascherson proposed the "Branchial theory", suggesting the imperfect obliteration of the pharyngeal cleft as the cause of these cysts. But in 1886 he proposed his "Precervical Sinus Theory" saying that these cysts were related to the cervical sinus rather than the pharyngeal clefts or pouches. 
Fig 1 : Branchial cyst in the left posterior triangle - As seen from the front
Wenglowski in 1912 in his dissection of cadavers found that no pharyngeal cleft tissue was found below the level of the hyoid bone and thus pointed out the inability of the "branchial theory" in explaining the cysts in the lower neck. He proposed the possibility of incomplete obliteration of the thymopharyngeal duct.
Based on the findings of Lucke and Luschka, King proposed the "Lymph node theory". Bhasker and Bernier, after their histological study of cysts concluded that these cysts developed due to cystic transformation of cervical lymph nodes. Maran and Buchanan arrived at the same conclusion however they also pointed out that such a transformation was not known to occur in any other site. 
Fig 2 : Branchial cyst in the left posterior triangle - Lateral view
There was a lot of speculation about the possible origin of the epithelium within the lymph node that led to the cystic transformation of the node and eventually formed the lining of the cyst. Bhasker and Bernier suggested 3 possible sources, the branchial cleft, the pharyngeal pouch and the parotid gland. [1-4]
Wilde and Mischke  ,  studied the keratin content of the epithelial lining of the cysts and found it homologous to the keratin content of the upper digestive tract epithelium, particularly that of the palatine tonsils. This was further confirmed by Stoll7 who injected blue dye into the tonsillar fossa of 3 cases preoperatively and found the distribution of stain within the capsule of the cyst during surgery. Hosemann after his study of the histopathological characteristics of the cyst epithelium, found it similar to the tonsillar epithelium. 
Fig 3 : Brillant Transillumination of the cyst
Although both the branchial cysts and fistulas were regarded to be of branchial origin now it is believed that "branchial cysts" have a non-branchial origin. [9-13]
The median age of presentation of these cysts is in the 3rd decade. They are found to occur more commonly in females.  ,  They have classically been described to occur anterior to the upper third of the sternomastoid.  However they have been reported to occur in the other areas of the neck, , as well as in the oral cavity,17-19 within the salivary glands, , [20-23] the thyroid24 and even in the mediastinum 25 and within the pancreas. 
Within the neck they occur most commonly in the region anterior to the upper third of the sternomastoid, followed by the region to the middle and lower third of the sternomastoid. It very rarely occurs in the posterior triangle of the neck. Most of the cysts occur deep to the investing layer of the deep cervical fascia and none of them have a cord or tract attached leading to the skin or the pharynx. , , , 
On microscopic examination these cysts are composed of a wall of lymphoid tissue lined with squamous or columnar cells. ,  , Due to the variability of the position King suggested that any cyst arising outside the midline, with the histological features as above should be regarded as a lymphoepithelial or a branchial cyst. 
Sites of branchial cysts in the neck
Titchener and Allison
Golledge and Ellis
Neel and Pemberton
Bhasker and Bernier
Ant. to Upper 1/3 of SCM
Ant. to Mid and Lower 1/3 of SCM
Submandibular r Region
Langlois  has described pancreatic tissue in a lateral cervical cyst, while Gosain and Wildes found gastric epithelium within a branchial cyst. There have also been reports of secondaries from papillary thyroid cancers and tonsillar cancers masquerading as branchial cysts, but such cases are rare. Most cases present with a painless, soft, cystic and brilliantly transcluscent swelling in the neck. Rarely is a cyst painful. 
Although clinical diagnosis of a cyst in the classical position is relatively simple. They are seldom correctly diagnosed preoperatively at other sites. Titchener and Allison  could make a correct preoperative diagnosis in only 22 out of their 42 cases, and have stressed on the role of preoperative ultrasonography of the neck and FNAB for evaluation of such cases. Earl31 has also found USG to be very helpful in the diagnosis of cystic neck swellings. The role of FNAB and preoperative CT scan of the neck has also been discussed by Rossell. 
Most patients are cured by complete surgical excision 9 of the cyst and usually never get a recurrence  and surgery remains the mainstay in the treatment of lateral cervical cysts. Unlike cystic hygromas there are no reports of any use of sclerosing agents or other drugs like OK432 or bleomycin in this condition.
As per King’s criteria any cyst arising outside the midline of the neck and having lymphoepithelial characteristics should be regarded as a branchial cyst. Such cysts are found more commonly in females and usually occur in the 2nd or 3rd decade of life. They are most commonly found in the anterior triangle of the neck anterior to the upper third of the sternomastoid. A cyst occupying the posterior triangle is extremely rare. However these cysts have been reported to occur in all the regions of the neck, and even in the mediastinum and the abdomen. Hence they should be suspected in all the cystic swellings of the neck except the median ones. Ultrasonography and FNAB definitely help in arriving at the diagnosis and is especially recommended for patients in the older age group to rule out cystic secondaries from head and neck malignancies. On operation a unilocular cyst with clear fluid, deep to the investing fascia and without a connecting stalk more or less makes the diagnosis certain. The histological picture is classical and confirmatory.
The ‘Branchial theory’ has now fallen into disfavour and the most appropriate hypothesis explaining the aetiology of these cysts is the "Lymph node inclusion theory" with he palatine tonsils as the most likely source of the enclosed epithelium.
Complete surgical removal remains the only acceptable form of treatment.
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