Novel technique using tensor fascia lata graft to reconstruct a floor of mouth postablative defect from invasive ectopic papillary carcinoma of the thyroglossal duct tract

Abstract

We describe a rare case of ectopic papillary thyroid cancer in the thyroglossal duct tract invading the floor-of-mouth musculature. The postablative defect was reconstructed with a bone-anchored tensor fascia lata graft to resuspend the floor of mouth to the mandible as a neogeniohyoid sling, enabling maintenance of a functional tongue position for normal speech and swallowing. This reconstruction should be considered when suprahyoid musculature is resected without breaching the oral lining.

Introduction

Thyroglossal duct cyst is the most common congenital neck anomaly and carries a 1% incidence of carcinoma; of these, 90% are papillary carcinoma, carrying a 95% overall 10-year survival.¹ Advanced local spread within the floor of the mouth is extremely rare and, to our knowledge, this is the first reported case where tumour invaded the suprahyoid muscles. We present this case and our previously undescribed method of reconstructing a functional floor of mouth with a bone-anchored tensor fascia lata hammock graft.

Case history

A 21-year-old woman presented with a 10-year history of an asymptomatic suprahyoid mass of static size. Examination revealed an irregular lesion above the hyoid bone that moved on tongue protrusion and swallowing. Magnetic resonance imaging showed a 3-cm irregular lesion in the suprahyoid region. On ultrasound, this lesion had microcalcifications. Fine-needle aspiration cytology was inconclusive. The thyroid multidisciplinary team recommended wide local excision and Sistrunk’s procedure. Intraoperatively, the mass was found to infiltrate geniohyoid, mylohyoid and both anterior digastric bellies. Frozen sections were sent and definitive surgery postponed until histological diagnosis, which confirmed ectopic papillary cell carcinoma in a thyroglossal duct cyst. Resection of the floor-of-mouth musculature, hyoid bone, strap muscle sections (fig 1), total thyroidectomy (fig 2) and bilateral selective neck dissections followed. The defect caused an unsupported floor-of-mouth defect in the submental and submandibular triangles measuring 10 × 8 cm, with intact oral lining (fig 3).

Figure 1.

Floor-of-mouth (FOM) resection, including thyroglossal cyst duct (TGCD), suprahyoid musculature, hyoid bone and cranial end of the strap muscles.

Figure 2.

Thyroidectomy specimen.

Figure 3.

Worm’s eye view of the 10 × 8 cm postablative floor-of-mouth (FOM) defect.

The floor-of-mouth muscular defect was reconstructed immediately with a reverse-planned tensor fascia lata graft that was tensioned along the inferolingual mandibular border with four mini-Mitek (DuPuy Synthes) bone-anchored sutures, creating a hammock suspension for the tongue base. The posterior graft edge was also tensioned in neck extension to the cut ends of the strap muscles and superficial thyroid perichondrium to reconstruct the mandibulolaryngeal complex (fig 4).

Figure 4.

Reconstruction of the floor of the mouth with Mitek (DuPuy Synthes) bone-anchored tensor fascia lata (TFL) suspension graft.

Histology confirmed a pTx, N1b classical papillary carcinoma from ectopic thyroid tissue, with hobnail micropapillary pattern, excised with clear margins. Within the neck, 1/63 lymph nodes was involved on the right with extracapsular spread, 0/52 involved on the left and 0/21 involved in the central compartment. No malignant focus was identified in the thyroid itself. The patient received radioactive iodine treatment and thyroxine (150 mg/day). Postoperatively, she was intubated and then underwent tracheostomy to facilitate extubation. Nasogastric tube feeding was replaced with fluids and diet after three weeks, and she made an uneventful postoperative recovery. Her video fluoroscopy at three months demonstrated the tongue maintained in a functional position (fig 5), with safe and functional oral, pharyngeal and oesophageal swallow phases (fig 6). Her speech recovered fully from transient left vocal cord palsy. Four months after surgery, oropharyngeal and nasoendoscopic examinations were normal.

Figure 5.

Lateral video fluoroscopy image demonstrating the tongue in a functional position supported by the floor-of-mouth reconstruction.

Figure 6.

Contrast swallow showing normal oral, pharyngeal and oesophageal phases.

At 10 months, iodine scan showed no abnormal uptake. The tensor fascia lata reconstruction on computed tomography at 10 months was viable, with normal resting position of the tongue and floor-of-mouth content (figs 7 and 8). At one year, she had normal a neck contour and no herniation of the floor of mouth through the reconstruction.

Figure 7.

Computed tomography sagittal section showing intact tensor fascia lata (TFL) reconstruction suspending the floor of the mouth (FOM).

Figure 8.

Computed tomography coronal section showing intact intact tensor fascia lata (TFL) reconstruction suspending the floor of the mouth (FOM).

Discussion

This is a rare presentation of a locally advanced thyroglossal duct cyst papillary carcinoma involving the floor of the mouth. The floor-of-mouth ‘diaphragm’ consists of the mylohyoid, digastric and geniohyoid muscles providing dynamic structural support for speech and swallow.² This muscular ‘diaphragm’ attaches to the hyoid bone and suspends the hyolaryngeal complex to the mandible, providing anterior traction to the epiglottis and flexing it under the tongue when swallowing. Ablative disruption of the hyolaryngeal complex increases aspiration risk,³ mandating its reconstruction.

Zhang et al described static reconstruction of the mylohyoid sling and floor of mouth with the vascularised tensor fascia lata component of a free anterolateral thigh flap. Static reconstruction of the floor-of-mouth mylohyoid diaphragm using synthetic Marlex mesh (Bard® Mesh Inc.) has not gained popularity, owing to infection risk and foreign-body reaction.⁴ In our technique, the suprahyoid muscular diaphragm was reconstructed with autologous tensor fascia lata graft suspended to the laryngeal cartilage to recreate a tensioned neomylohyoid sling and mandibulolaryngeal support complex. The floor-of-mouth defect did not require vascularised tissue transfer for oral lining reconstruction or tongue base obturation.

Tensor fascia lata harvest has been well described, with the thickest available proximally and laterally as a continuation of the iliotibial band.⁵ Tensioning the tensor fascia lata with bone-anchored sutures along the inferolingual mandibular border ensured a robust fixation. Consideration for the inferior lingual nerve coursing through the mandibular medulla is required to avoid injury and numbness of ipsilateral dentition, chin and lower lip. The posterior margin of the reconstruction must be anchored to laryngeal fascia in neck extension to prevent gravitational descent of the laryngeal complex.

Conclusion

Papillary carcinoma of the thyroglossal duct cyst is a rare presentation of an anterior neck lump. When tumour invades the floor of the mouth, resection of the mylohyoid sling causes speech and swallow dysfunction. We describe for the first time a bone-anchored, tensioned, functional mylohyoid sling reconstruction using autologous tensor fascia lata graft that avoids the problems of synthetic meshes. We recommend this technique for extraoral floor-of-mouth defects of the suprahyoid muscles.