CASE SERIES: VARIATIONS IN THE EMBRYOLOGY OF CONGENITAL MIDLINE CERVICAL CLEFTS

CASE REPORTS

Case 1

A 4-month-old Caucasian male infant presented to the department with a midline cervical cleft, which had been present since birth. The infant was born full-term by a normal vaginal delivery. The pregnancy was uncomplicated and there was no relevant maternal history, antenatal investigations were also normal. There was a family history of a thyroglossal cyst, present in a fellow sibling.

The cleft was situated in the midline between the symphysis menti and suprasternal notch. It consisted of a skin tag, an area of friable epithelium and a sinus tract extending to the suprasternal notch. The friable area had previously bled intermittently and the midline of the mandible was noted to be notched. There was no contracture of the neck and the infant did not appear to be troubled by the cleft.

There were no other dysmorphic features and a full examination was otherwise unremarkable apart from a slightly low weight, which had been a problem since birth. Ultrasound of the neck demonstrated a normal thyroid gland.

Subsequent surgery consisted of an excision of the midline cleft and primary closure with a local flap. The area of friable epithelium and the sinus tract was excised with an elliptical incision. The midline skin tag was divided in half in the sagittal plane and excised creating two lateral flaps for closure. There were no significant post-operative issues.

Case 2

A 12-week-old female Caucasian infant presented to the department with a midline ventral cervical cleft. The baby was born prematurely at 33 weeks and delivered by a normal vaginal delivery. At birth the baby was in respiratory distress and was ventilated for 10 days, with parenteral nutrition being given for 7 days. Other noted conditions were a patent ductus arteriosus. The thyroid function tests were noted to be normal at birth. There was no family history of note. Surgery consisted of excision of the mucosal track, using part of the accessory ‘tag’ as two transposition flaps. Z-plasties were also used to break up the vertical linear scar (Fig. 1–5).

Pathology

The specimens were fixed, sectioned and stained with haematoxylin and eosin.

Histology from the first case showed epidermis and dermis with some attached subcutaneous tissue. The sinus tract was lined by ciliated pseudostratified columnar epithelium (Fig. 6, 7). This was also concluded to be bronchogenic in origin with no features of atypia.

The specimen from the second case contained a cutaneous tag devoid of adnexal structures, the distal part of the specimen consisted of a non-ciliated columnar epithelium opening into a more dilated cystic structure lined by pseudo-stratified columnar epithelium (Fig. 8).

DISCUSSION

CMCC is a rare anomaly of the ventral neck that may present at any level between the mandible and manubrium. They appear to be sporadic in the patient’s families and more commonly affect Caucasian females (7).

Histologically, the cephalic skin tag consists of epidermis with occasional bundles of skeletal muscle in the core. The mucosal surface consists of a stratified squamous epithelium surface with an absence of skin appendages. The caudal sinus can be lined with pseudostratified columnar epithelium or squamous epithelium (absence of ciliation) indicating a branchial origin. The sinus can also be lined with ciliated pseudostratified columnar or squamous epithelium, the presence of ciliation indicates a bronchogenic origin.

Bronchogenic cysts have a cuboidal or columnar, ciliated pseudostratified epithelial lining, commonly squamous metaplasia can occur following infection, as in our first case. Other structures invariably present in the cyst wall are blood vessels, hyaline cartilage, smooth muscle, seromucinous glands and elastic fibres (8). They can occur in the mediastinum, along the tracheobronchial tree or peripherally in lung parenchyma. Location in the subcutaneous tissues is rare (9). When subcutaneous they present as a soft swelling or draining sinus in the suprasternal notch or supraclavicular area.

The extra-thoracic subcutaneous location of bronchogenic cysts is thought to arise by the pinching off the pulmonary trunk during the embryonic development of the sternum. The laryngotracheal groove separates the primitive foregut into ventral (tracheal) and dorsal (oesophageal) structures beginning in the 5^th week of gestation. The ventral portion gives rise to the trachea and major bronchi. The sternum arises by the fusion of lateral cartilaginous plates, during this process pulmonary parenchyma may protrude through the gap and become pinched off as the bars fuse completely by the third month in utero forming a bronchogenic cyst (8).

Both of our reported cases have the clinical features of CMCC, with the first case appearing to be bronchogenic in origin and the second case appears to be solely branchial in origin due to the absence of ciliation.

Failure of midline fusion of the branchial arches are thought to be responsible for the spectrum of branchial arch anomalies. If this involves the second cleft it may lead to an isolated cervical cleft. The branchial arches form part of the branchial apparatus, which consists of embryonic ectoderm, mesoderm and endoderm and is responsible for forming the head and neck structures. Development of the apparatus begins during the second week of gestation and is completed by week 6–7. The apparatus consists of five branchial arches appearing at the lateral wall of the foregut, separated from each other externally by ectoderm-lined branchial clefts and internally by endoderm-lined pharyngeal pouches. The arches are numbered 1, 2, 3, 4 from cranium to cauda; the 6^tharch does not appear externally and is only represented by a mesodermal core (Fig. 9).

Theories for the failure of midline fusion include increased pressure of the pericardial roof on the most distal branchial arches in the early stages of the developing embryo (30^th–35^th day) resulting in necrosis and ischaemia. At this stage separation of the respiratory system from the digestive system is occurring and a disturbance in this area is likely to affect both systems (6). Another theory is the rupture of a pathological adhesion between the epithelium of the cardiohepatic fold with that of the ventral part of the first branchial arch (10).

The real question is the whether the clinical picture of CMCC originates from a branchial developmental abnormality in-utero or are the previous reported cases actually bronchogenic in origin with squamous metaplasia accounting for the squamous component. From a review of previously reported cases, the histology has undoubtedly had some respiratory components in the majority. We have reported on two theories which account for the abnormality in the second branchial arch and CMCC and one theory which accounts for bronchogenic defects in isolation. There appears to be much variability in CMCC, with it either being solely branchial or solely bronchogenic or both. No satisfactory theory accounts for how they can exist together and some of the previously reported cases do not clearly differentiate the histology and the two entities leading to erroneous nomenclature.

CONCLUSION

We report on two cases with the clinical diagnosis of CMCC, the embryology of the first case suggests a bronchogenic component with squamous metaplasia and the second case indicates a solely branchial origin. This indicates the variability in the embryonic origin of a clinical CMCC, implying that this is spectrum of disorders with variations on the same theme. The recommended treatment is complete excision for cosmetic reasons and to overcome restricted neck extension due to fibrous midline cervical webbing. It may be difficult to categorically prove the embryological cause for this clinical entity but by identifying more cases the importance of raising awareness of this condition has relevance to plastic surgeons, otolaryngologists and maxillofacial surgeons.

Acknowledgements

We woud like to thank Dr Ruth Nash and Dr Heung Chong, Consultant Histopathologists, St. George’s Hospital, for their much appreciated comments. We also thank Dr Anand Saggar, Consultant Geneticist, for his valued advice.

Address for correspondence:

Miss Dulani Mendis

Dept. ENT Surgery, University Hospital Coventry

Coventry CV2 2DX

United Kingdom

E-mail: dulanimendis@yahoo.com