Pharyngeal arches and its anomaly

slideshow of pharyngeal arches and its development and various anomalies assosciated with it and its its classification and management.

1. pharyngeal arches and its anomaly DR. AYUSHREE DR N.K. SINGH SIR UNIT ( ENT-IIB)

2. PHARYNGEAL ARCHES Pharyngeal arches are also known as branchial arches because of their evolutionary origin supporting the gills in the earliest vertebrates. Many of the changes seen during development of the mammalian pharynx reflect the functional evolutionary origins of this region. As successive populations of neural crest cells migrate around the pharynx at progressively more caudal levels, five pairs of pharyngeal arches are formed. This process is complete by stages 14–15 (5 weeks). Pharyngeal clefts (grooves) separate the arches externally; they are matched internally by internal depressions, the pharyngeal pouches. Each pharyngeal arch consists of epithelial covering, ectoderm externally and endoderm internally and endoderm internally, filled with mesenchyme that is mainly of neural crest origin, with a contribution from primitive streak derived mesenchyme (paraxial mesenchyme). The neural crest cells of each arch form a skeletal element and associated connective tissue; they also give rise to the walls of an aortic arch blood vessel, which is lined with endothelium derived from angiogenic mesoderm. Paraxial mesenchyme also forms the muscle associated with each pharyngeal arch.

3. 1st branchial cleft sinus ( <10%) -The external opening in the neck varies in position but lies on a line between the tragus and the hyoid bone. The opening is often inconspicuous and appears as a skin-lined pit. -The superior attachment of the sinus is variable: there may be an opening anterior to the tragus or the tract may form a true fistula running inferior to the floor of the EAC and opening at the osseocartilaginous junction in the external auditory meatus or rarely forming a frenulum-like band between the floor of the meatus and the umbo of the tympanic membrane.

4. Histology The sinus (sometimes known as a collaural fistula) is usually a sizeable tract, often formed of cartilage, and lined with squamous epithelium. The original classification by Work and Work2 divides them into two types according to the presence or absence of mesothelial elements within the wall. • Type I lesions are of ectodermal origin and are present medial to the concha. They are usually superficial and simple in nature. • Type II lesions are both ectodermal and mesodermal in origin and contain cartilage and hair follicles. The more inferior opening of the type II fistula is usually below the angle of the mandible and the tract is intimately related to the facial nerve trunk.

5. PRESENTATION : The opening is present at birth and may become more obvious by the discharge of epithelial or sebaceous debris. The sinus may become acutely infected and may progress to abscess formation. Being lined with skin, these lesions do not discharge mucus. INVESTIGATION : Cross-sectional imaging will usually show the tract, which is often substantial in calibre but will not clearly demonstrate its relationship to the facial nerve. MRI is preferable over CT but still one can go multi slice helical CT. TREATMENT : INDICATION :Surgical excision of these lesions is usually advocated if at all symptomatic or if one or more episodes of infection have already occurred. CONTRAINDICATION :Surgery is ill-advised during acute infection and a period of quiescence should be awaited followed by elective excision

6. 1. A parotidectomy-type incision is modified to include the lower opening of the sinus. The sinus tract at this point can be followed for a small distance upwards; when its nature and direction are confirmed. 2. The facial nerve trunk must be identified as it leaves the skull base and enters the parotid gland. The mandibular branch in particular should be followed so that it can be preserved while freeing the tract. Sharp dissection will often be required to free the nerve from the tract, particularly if multiple infections have ensued or previous attempts at incision and drainage have been made. In most instances the lesion will run deep to the branches of the facial nerve, which may be adherent if there has been recurrent infection, though the relationship is unpredictable. 3. The superior part of the sinus tract also has an unpredictable relationship to the cartilages of the external auditory canal (EAC). It may terminate at the canal or may form a duplicated canal parallel and inferior to the EAC proper.

7. 4. The lesion does not extend medial to the cartilaginous canal but a strand may cross the lumen of the canal from the osseocartilaginous junction to be attached to the umbo. Facial nerve exposure and protection is required in nearly every case of first branchial cleft sinus. If this is done, then risk to the facial nerve is minimized. 5. The upper end of the lesion must be followed and excised to ensure that no squamous epithelium remains, and this may require opening of the EAC and use of the otological microscope and ear instruments. 6. Closure of the wound with suction drainage and, if necessary, light packing of the ear canal completes the operation

8. SECOND BRANCHIAL CLEFT SINUSES (90%) The second branchial arch forms the epidermis of the upper neck and dorsal pinna. The mesoderm forms the facial muscles and the body of the hyoid, and the endodermal elements form the root of the tongue, the foramen caecum, the thyroid stalk and the tonsil. The second branchial cleft sits immediately caudal to these structures and it is persistence of this cleft that leads to the formation of the second branchial arch sinus. Second branchial arch sinuses may be associated with branchio- oto -renal syndrome, especially if bilateral. The second branchial cleft sinus presents as a congenital opening on the lower neck, anterior to the sternocleidomastoid muscle. The tract of the second branchial cleft sinus is directed proximally and medially to pass between the internal and external carotid arteries. The proximal end may communicate with the pharynx through the palatine tonsil to form a true fistula in some cases, although most lesions are not patent through their whole length. The sinus nearly always leaks clear or mucoid fluid from the distal external opening due to secretions from ectopic salivary tissue in the wall of the sinus itself rather than any leakage from the pharynx. They typically present as a spherical swelling inferior to the angle of the mandible, anterior to the sternocleidomastoid, although other unusual locations occur.

9. BAILEYS CLASSIFICATION : • Type I: deep to platysma, anterior to sternocleidomastoid • Type II: abutting internal carotid artery and adherent to internal jugular vein (most common) • Type III: extending between internal and external carotid arteries • Type IV: abutting pharyngeal wall and potentially extending superiorly to skull base

10. INVESTIGATION : As a rule with second branchial cleft sinuses, the diagnosis is evident and no further investigation is required. Neck ultrasonography can characterize the size of tract or associated sharply demarcated cyst, and renal tracts can be imaged to exclude horseshoe or duplex kidney. However, a radiopaque sinogram is not routinely indicated. Cross-sectional imaging will usually show the close relations of a second branchial cyst and is particularly helpful for type III or IV presentations. MRI is preferable to CT in children to minimize exposure.

11. TREATMENT : Because of the risk of infection, excision of second branchial cleft sinuses is advisable. Surgery can be performed at any age and aims to excise the tract completely when no infection is present. A fusiform skin incision is made around the external opening and the tract can be followed upwards with microbipolar dissection and counter traction with lacrimal retractors. If the distance between the external opening and pharynx is too great to allow good access, a second stepladder incision is made superiorly in the neck to enable the cranial portion of the tract to be visualized and excised. The tract will be seen to enter the pharyngeal muscle at the level of the palatine tonsil and can be ligated and excised at this level. Although ipsilateral tonsillectomy is unnecessary in the vast majority of cases, tonsillectomy should be considered in the larger type IV second branchial cleft cyst that abuts the pharynx . Care must be taken to avoid the hypoglossal nerve in the superior part of the dissection. Complete excision of the sinus should prevent recurrence. Surgery for second branchial cleft cysts should be planned when infection has resolved, taking care to avoid injuring the internal jugular vein and hypoglossal nerve superiorly.

12. Third & fourth pharyngeal pouches sinus (1-2%) Third and fourth pharyngeal pouch sinuses are rare abnormalities, accounting for 1–2% of branchial lesions, which can present as a sinus, cyst, thyroid gland abscess or even a fistula from pharynx to skin. They almost always occur on the left side. They tend to present in early childhood with associated infections or in neonates with airway obstruction. The third and fourth branchial arches are related to the thyroid, parathyroid and thymus and therefore tracts may course close to or through these structures: both originate at the pyriform sinus. The third arch is associated with the glossopharyngeal nerve whereas the fourth is related to the superior laryngeal branch of the vagus nerve. This can explain the theoretical course of third and fourth pharyngeal pouch anomalies, however case reports to demonstrate these are lacking.

13. 3 rd pharyngeal pouch presenting as a cystic swelling on left side of hyoid bone   4 TH pharyngeal pouch presenting as a draining neck wound on the anterior portion of the patient’s left sternocleidomastoid muscle.

14. PRESENTATION : These anomalies present most commonly with some form of infection, often recurrent thyroid abscess, which is treated with incision and drainage without recognition of the diagnosis and rendering recurrence inevitable. INVESTIGATION : Various investigations have been proposed: barium swallow, radioiodine scan, ultrasonography and CT. However, MR imaging alone is suitable followed by rigid endoscopy under anaesthesia to identify an opening in the pyriform sinus. TREATMENT : Although wide-field extirpation of the cyst, tract and ipsilateral thyroid lobe using a hybrid open and endoscopic approach to the pyriform sinus was the standard treatment, modern management utilizes endoscopic cautery of the pyriform fossa sinus alone as first-line treatment. Bailey described successful endoscopic diathermy of the pyriform fossa opening in two cases in 2004 which has become first-line treatment to obliterate the tract and avoid recurrent infection. Garabedian recognized a higher recurrence rate in neonates in a series of 20 children and recommended resection via open approach rather than endoscopic approach in this younger age group.

15. TREATMENT : If the sinus or cyst is symptomatic, local excision is the treatment of choice. The sinus is explored under general anaesthetic with a lacrimal probe which usually shows deep extension towards the roof of the ear canal for 10 mm or more. The punctum is excised with a fusiform skin paddle and excised in continuity with the entire tract, which is usually adjacent to the underlying cartilage; excising a portion of this reduces the risk of recurrence. Some will use methylene blue to guide dissection but others avoid this in case of spillage into the field, which makes dissection more awkward.

16. Thyroglossal duct cyst Thyroglossal duct cysts are the most common congenital abnormality in the head and neck region. The thyroid develops from the foramen caecum, which lies in the midline of the tongue at the junction of the anterior two-thirds and posterior one-third. In normal development, the thyroid descends through the tongue, passing caudally with an intimate relationship to the hyoid bone and finishing in the anterior neck overlying the trachea and laryngeal cartilage. In around one-third of cases the duct has been found posterior to the hyoid bone, which has important implications in surgical treatment. The duct may fail to involute during the weeks 8–10 of gestation and as a result an abnormal cyst may arise anywhere along the tract and may contain thyroid tissue.

17. PRESENTATION Despite being a congenital lesion, thyroglossal duct cysts often present later in childhood or early adulthood. The complaint is usually of a midline swelling in the neck although it can occur laterally, usually left sided in around 10% of cases. The mass elevates on swallowing and tongue protrusion. It may present with a complication of infection or fistula formation to the skin if surgically drained. INVESTIGATION It is possible for the thyroglossal cyst to contain the only functioning thyroid tissue and therefore removal would result in hypothyroidism. Ultrasound is useful in confirming the diagnosis and the presence of a normal thyroid gland in the usual position. Cross-sectional imaging before revision surgery is advised to ascertain an intact hyoid bone or localize recurrent cyst.

18. TREATMENT It is nearly always surgical excision unless the cyst is very small and asymptomatic. If a fistula to the skin is present, this is excised with the underling cyst and tract. The definitive operation is that described by Sistrunk from the Mayo Clinic in 1920,9 removing with the thyroglossal duct a portion of the hyoid bone, a portion of the raphe joining the mylohyoid muscles, a portion of each genioglossus muscle and the foramen caecum. If the surgery is performed as he described, recurrence rates can be kept below 5%; this was confirmed in a 2013 systematic review including 750 patients having primary surgery. Problems arise where there has been a deviation from Sistrunk’s procedure resulting in an incomplete resection. Recurrence rates following incomplete excision rise to 27%. The  operation  has  been developed further with an extended or modified Sistrunk procedure, which involves a wider block dissection incorporating the infrahyoid region to the thyroid isthmus initially used for recurrent disease but now applied to all patients to minimize complications. Complications include haematoma , seroma, cyst recurrence, salivary fistula and hypoglossal nerve injury.

19. Lingual thyroid Lingual thyroid is the result of failure of descent of the thyroid anlage from the foramen caecum of the tongue. It is a rare entity with prevalence of 1 : 100 000. Girls are more commonly affected.12 In 70–80% of these cases, the lingual thyroid is the only thyroid tissue present. Up to one-third have hypothyroidism. Malignancy has been reported and seems to carry the same risk as thyroid in a normal cervical location. PRESENTATION Depending on size, lingual thyroid can present with dysphagia, airway obstruction, haemorrhage or endocrine dysfunction. More often the patient is completely asymptomatic with suspicion only after other investigations, following routine ENT examination or detected on parental curiosity. INVESTIGATIONS Imaging will confirm lingual thyroid with either CT or MRI. Although MRI is preferred to avoid ionizing radiation. In addition to the lingual thyroid, imaging is used to identify if there is thyroid tissue in the normal cervical location. Ectopic thyroid has been reported in the oropharynx, larynx, infrahyoid neck, mediastinum, oesophagus and heart. Technetium (99mTc) thyroid scan will identify metabolically active thyroid tissue in the tongue base and no uptake in the neck. Thyroid function tests are usually normal but up to a third of patients demonstrate hypothyroidism; hyperthyroidism is rare.

20. TREATMENT For small, asymptomatic lingual thyroids, suppression with TSH may be effective in checking growth. Reduction is often slow and dramatic results should not be expected. Paediatric endocrinology input is essential. Use of radioactive iodine for thyroid ablation is generally avoided in children. Surgical excision is occasionally required when significant obstructive symptoms are present or repeated or severe haemorrhage is an issue. Transoral resection is usually possible using nasotracheal intubation. For larger and deeper lesions, an external approach may be required. This may even necessitate planned tracheostomy for large masses where swelling and obstruction are inevitable. Lifelong monitoring of thyroid function is essential.

21. CONGENITAL MIDLINE CERVICAL CORD AND CLEFT EMBRYOLOGY Congenital midline cervical cord/cleft (CMCC) is a rare congenital abnormality forming on the anterior neck which may extend to the mediastinum. It was first described by Bailey in 1924. AETIOLOGY : It is unclear but it is felt to arise due to failed midline fusion of the second and third branchial arches. PRESENTATION : CMCC may present at birth with a cleft extending from the mentum to the sternum. There may be no external defect seen but a characteristic ‘cord’ seen or palpated below the skin when the neck is extended. If a cleft is present, serous discharge may be evident and the upper end will have a pseudonipple appearance. IMAGING CT or MRI allows characterization of the location and depth of the tract and differentiation from other midline congenital lesions. TREATMENT If there is no skin breakdown and the patient is asymptomatic, a conservative approach may be adopted. Surgery is indicated for cosmetic reasons and prevention of cervical contractures. Elective surgical excision is advocated using stepladder horizontal incisions or Z- plasty closure to avoid contracture.

22. SINUS STERNOCLAVICULARIS PRESENTATION Sinus sternoclavicularis is usually present at birth with an asymptomatic sinus at or near the sternoclavicular joint, more often on the left side. IMAGING Ultrasound allows characterization of the location and depth of the tract and confirmation of normal thyroid gland. Often no further imaging is required. TREATMENT If there is no skin breakdown and the patient is asymptomatic, a conservative approach may be adopted. Elective surgery is indicated for cosmetic reasons, usually involving excision of a blind-ending sinus which peters out adjacent to the sternoclavicular joint.

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