Presentation and Diagnosis
ECT in children generally presents as an asymptomatic lateral neck mass. Symptoms can occur as a result of infection,4, 18airway obstruction,5, 6, 34, 39 feeding difficulties,46, 49 and rarely Homer syndrome.50 We detected a significant higher incidence of lesions located in the neck (79%) and in the male population (79%). The lesion has also been described as an incidental finding in paediatric autopsies with an incidence as high as to 31%.79 Rarely, ECT has been found in the autopsies of children after sudden infant death syndrome although no clear correlation has been identified with this.3 In a review of autopsies with an incidental finding of cervical ectopic tissue the ECT size demonstrated a negative correlation with age (r = -0.75; p = 0.034) suggesting that the lesion may disappear over the first few years of life.44
The differential diagnoses in children include; congenital or acquired neck lumps such as dermoid and sebaceous cysts, thyroglossal duct cysts and branchial remnants. USS is useful in the characterisation of ECT and is now considered the first-line investigative modality.71 Sonographically, thymic tissue is identified by a homogeneous, hypoechoic mass with internal echogenicities.10, 56, 71 However, despite the presence of internal echoes in our case, the initial report suggested the lesion to be a branchial cleft cyst. Overall, definite diagnosis, leading to a conservative management was obtained in 30 (21%) patients. For the 106 ECTs that were surgically excised, including our case, ECT was not listed as a preoperative differential diagnosis. This suggests that ECT is rarely considered in the differential diagnosis of neck masses in children. Several authors have highlighted the challenges in the pre-operative diagnosis of ECT mimicking other abnormalities such as branchial cysts,18, 29, 31, 32, 37, 49lymphatic malformations,18, 20, 29, 31, 77haemangiomas,29 hamartoma,37thyroglossal duct cysts,18, 77teratoma,46, 77 lymphoma,47, 59neuroblastoma,54 and dermoid cysts.37
For clinically ambiguous cases, MRI has proven to be a superior radiological modality to both characterize these lesions and document any additional ectopic thymic tissue. It also confirms the presence of continuity between the ECT and a mediastinal thymus, or the presence of a normal mediastinal thymus.13 Thymic tissue is identified by a homogeneous, isointense on T1 weighted images and hyperintense on T2 weighted images.56 The signal intensity is similar for ECT and orthotopic thymus.13
Diagnosis can also be helped by FNA or incisional biopsies. Tunkel et al. documented that FNA can accurately diagnose ECT based on presence of fibrous septa, Hassall’s corpuscles, and other characteristics of normal thymic architecture.16 However, ECT has been erroneously diagnosed on FNA as lipoblastoma,19branchial cysts33, 66 and lymph node tissue/lymphoma.9, 33, 68 Incisional biopsy might also be misleading and some authors have also highlighted the challenges related to histological diagnosis with incisional biopsies reported as infected/chronic inflammatory masses, vascular anomalies and lymphomas.8, 15, 47 Similarly, in our patient the incisional biopsy documented xanthogranulomatous inflammatory change and fibrosis.