Microtia

Innovating with 3D Bioprinting in Microtia Surgery

Prof Mukherjee’s microtia program commenced in 2015. She leads the only cartilage bioprinting research program for microtia in Australia. Awarded >8M in research funding, this program fosters some of Australia’s brightest engineers and clinicians undertaking Mphil, PhD and post doctoral research.

Prof. Mukherjee performs Australia’s First Paediatric OSIA Surgery

Prof. Mukherjee performed Australia’s first paediatric OSIA surgery, which was also performed alongside 3D printed porous polyethylene implant performed by Dr Joe Dusseldorp and Dr Nicholas Lotz .

About Microtia

The most common malformation (50%) affecting the head and neck, Microtia leaves patients deaf and with deformities impacting literacy and social development. The ear is divided into an outer, middle and inner ear. Microtia affects the development of the outer and middle ear structures. Surprisingly, the inner ear is seldom affected in Microtic patients unless the children have additional syndromes. This means that the most patients have a healthy cochlea and balance system. Hearing loss is usually mainly conductive in nature. If the conductive hearing loss is treated, then the patients often have very good perception of sound.

Microtia varies in severity from grade 1-4. Microtia can also be related to ear canal and middle ear abnormalities. If the ear canal is narrow but patent, there may be additional ossicular abnormalities (bones of the ear may be malformed) still creating a conductive hearing loss.

Grade 1: The ear is smaller than normal with minor abnormalities, but the key features of the normal ear are present.
Grade 2: Some of the features of the ear are missing, though usually much of the lower two-thirds of the ear is still present. The ear canal may be present, but frequently is very narrow (canal stenosis).
Grade 3: This is the most common type of microtia, in which the only feature remaining is a small peanut-shaped remnant ear lobe.  The ear canal is usually completely absent (aural atresia). This will cause maximal conductive hearing loss in the affected ear.
Grade 4: Complete absence of the external ear without any remnant. This is called “anotia”, and is rarely seen.

Microtia Treatment

Treatment requires attention to 2 aspects. Firstly, the functional aspect of treating the hearing loss ; secondly, the cosmetic appearance of the outer ear. In Australia,  the hearing reconstruction is done by an ENT surgeon with post-operative rehabilitation by an audiologist while the cosmetic aspect or microtia reconstruction is done by a reconstructive surgeon (plastics team).

In Australia, historically, the two surgeries were seldom performed together and therefore co-ordination of the care could be fragmented. However, with new technologies, care co-ordination has become easier, allowing surgery to be co-ordinated at the same time and performed younger.

Prof Mukherjee, performs combined hearing implantation surgeries in collaboration with Dr Joe Dusseldorp, a plastic surgeon, who performs microtia reconstruction with 3D printed porous polyethelyne implants

Options of Microtia repair

1: Traditional repair consists of reconstruction using cartilage harvested from rib graft. Typically, this is done between the age of 8-10 when the child is big enough to have rib cartilage large enough for donor graft and the child’s ear is almost of adult size.

3D printing has allowed new solutions:

2: 3D printed Medpor implant. Medpor is a non-resorbable material but can be manufactured in the shape of the contralateral (normal) ear. Since a donor graft doesn’t need to be harvested, the surgery may be performed at a younger age (such as age 4). 3D planning and virtual design is performed to ensure that the reconstruction is optimal. Performing this surgery this young also allows combining hearing implant surgery at the same time as the reconstruction. This also means that both the 3D printed ear and the implantable hearing aid can be inserted through one single incision.

3: Emerging technology: Bioprinting is a technology that involves 3D printing with stem cells or cartilage cells. In this case, cells are harvested either from the other (normal) ear or nose and cloned in the lab. These cells are then printed alongside a resorbable study biocompatible scaffold that will eventually be digested by the body.  The scaffold is 3D printed in the shape of the ear of the patient and provides support while the cartilage cells grow and mature to eventually take over the structural strength once the scaffold has been digested. This technology has already been clinically implemented. Therefore, it is a matter of years before it becomes more widely available to patients.

Hearing rehabilitation

Hearing is a really important part of a brain, linguistic and social development of any child. Although many parents are concerned about the impact on the child’s confidence because they of the cosmetic appearance of the microtia, hearing loss which is more commonly unilateral in microtia, will affect understanding speech in noisy environments such as playground and class room, leading to listening fatigue and lead to impairment of the child’s confidence and social development. Early access to sound has an important role in the child’s brain development and therefore it is important that hearing rehabilitation is seen as a priority for parents.

Hearing rehabilitative options include non-surgical and surgical. An audiogram (hearing test) and CT scan will often be performed so your doctor can discuss current and future options for treatment to suit your child’s needs.

Non-Surgical options:

Very early in the child’s life, children suffering from conductive hearing loss due to Microtia will be first offered non-surgical options until they are old enough to warrant surgery.

1: If there is an ear canal and ear drum, the patient may be able to wear a conventional hearing aid (especially if the remnant or repaired ear can hold a hearing aid). In Australia, anyone under 26 years of age have access to fully funded hearing aids through the Australian Government through Hearing Australia.
2: More commonly patients have complete ear canal atresia or are unable to wear a hearing aid (as the cartilage of the ear is too soft). Therefore, children with microtia are more commonly assisted with a bone conduction hearing device attached with a soft band by adult and children. These devices are made by different manufacturers and include:

1: Cochlear BAHA

2: Oticon Ponto

3: MeDEL Adhear

Surgical options:

1: Ear canal reconstruction: Outcomes of ear canal reconstruction or Atresiaplasty rely on the ability to create a ear canal that is self cleaning and waterproof and extent of abnormality to the middle ear structures. At best, the outcomes of Atresiaplasty has a 50% hearing improvement and commits the child to lifelong ear toilets. In the past, ear canal reconstruction was often used but with the advent of implantable bone conduction hearing devices, in Australia ear canal reconstruction has become less popular as surgery needs to be considered alongside risks to the patient especially when a good hearing outcome cannot be guaranteed. In particular, these risks include trauma to the facial nerve (the nerve responsible for supplying the muscles of the face) which often follows an abnormal course in patients with microtia (and therefore is at higher risk of injury). Secondly, in children with complete atresia, a new ear drum and skin lining of the ear canal needs to be created. The skin lining the ear canal is unique and has properties of migration which makes the ear canal self-cleansing. Thus, even if an ear canal can be created by drilling a hole, turning that into a healthy, self-cleaning, non-discharging ear that is able to conduct sound is extremely challenging in cases of complete atresia.

2: Implantable hearing aids: Bone conduction hearing aids include passive and active and passive implants.

Passive implants: Non-active implants include Bone anchored hearing aids. They can either be clipped onto a transcutaneous abutment which does not require a magnet such as the BAHA Connect or Oticon Ponto. However, common complaint of this system is possible skin irritation). To avoid an abutment which protrudes through the skin, a magnetic version of this can be used (BAHA Attract). However, there is loss of power through the skin and the hearing outcome is not as good as the direct coupling (BAHA Connect) or the active implants.

Active implants have evolved recently and include products such as the MEDEL bonebridge, Cochlear OSIA, Oticon Sentio. These devices do not protrude through the skin and have minimal wound infection risks. However, there is a magnet in the implantable device which communicates with an external speech processor which transmits the sound. The power and hearing outcome from these devices is much more superior to passive implants and by far, ongoing innovation in these solutions are now superceding a case for passive implants.

Placing active implants in young children can be challenging as they need enough bone thickness. 3D planning and printing has provided new options for prior planning of these procedures which your ENT surgeon may discuss with you.

Surgical Considerations 

Considerations into choice of device depends on the anatomy of the child, concurrent syndromes, other surgeries such as whether the child is undergoing combined microtia reconstruction and hearing rehabilitation or if these will be performed separately and future need for MRI scans.

Combined Microtia reconstruction and Implant insertion

The advantage of combined surgery include one surgery for both aspects as well as being able to do both procedures through one incision, expediting wound healing. When combined with 3D printed porous polyethylene implants, this surgery can be done as early as 5 years old. However, this technique relies on a temporoparietal flap that covers the 3D printed ear which further thins the skin overlying the implantable hearing aid. In general all current devices need a small amount of drilling of bone but there may also be soft tissue limitation if the child has very thin skin that may influence choice of device and surgical technique. Children with hemifacial microsomia or other children tend to have softer bone and thinner skin, which are additional considerations.

MRI considerations:

All active implants are MRI compatible but the conditional approval of the type of MRI compatibility varies as follows:

OSIA: conditional  compatibility with 3T MRI scans, with 7cm head shadow from MRI scan. Magnet can be removed from the device without the device explantation which will reduce the MRI shadow to 3cm.

BoneBridge: conditional compatibility with 1.5T MRI scans with a 15cm head shadow

Sentio: conditional compatibility with 1.5T MRI scans with 17cm head shadow

Prof Mukherjee’s Microtia Papers

1: Fay CD, Jeiranikhameneh A, Sayyar S, Talebian S, Nagle A, Cheng K, Fleming S, Mukherjee P, Wallace P. Development of a Customised 3D Printer as a Potential Tool for Direct Printing of Patient Specific Facial Prosthesis. The International Journal of Advanced Manufacturing Technology. https://doi.org/10.1007/s00170-022-09194-0 *Senior Clinical Author
2: Posniak S; Chung J; Liu X, Mukherjee P, Gambhir S; Khansari A, Wallace G. Bioprinting of chondrocyte-stem cell co-cultures for auricular cartilage regeneration. Open Science Publications. doi: 10.1021/acsomega.1c06102
3: Chung J, Kade J, Jeiranikhameneh A, Ruberu K, Mukherjee P, Yue Z, Wallace G. 3D printed structures for auricular cartilage reconstruction using hybrid printing. Biomedical physics and engineering express. (doi.org/10.1088/2057-1976/ab54a7). Accepted 2019 (*Senior clinical Author)
4: Chung J, Kade J, Jeiranikhameneh A, Yue Z, Mukherjee P, Wallace G. A Bioprinting approach to cartilage regeneration for microtia – review paper. Bioprinting. https://doi.org/10.1016/j.bprint.2018.e00031 (*Senior clinical Author)
5: Mukherjee P, Chung J, Cheng K, Gupta R, Haag H, Williams Z, Wallace G. Invitro and invivo study of PCL-Hydrogel scaffold: degradation pattern and biological response. Journal of Craniofacial Surgery. 2021, 32(5):1931-36:  DOI: 10.1097/SCS.0000000000007173
6: Mukherjee P, Cheng K, Wallace G, Chiaravano E, Macdougall H, O’Leary S, Solomon M. 20 year review of 3 Dimensional tools in Otology: challenges of translation and innovation. Otology and Neurotology 2020; 41(5): 589-595.
7: Mukherjee P, Clark J, Wallace G, Cheng K, Solomon M, Richardson A, Maddern G. Discussion paper on proposed new regulatory changes on 3D technology: A Surgical Perspective. ANZ Journal of Surgery. 2019; 89: 117-121. (Top downloaded paper Wiley 2018-19)
8: Kemp S, Coles-Black J, Walker MJ, Wallace G, Chuen J, Mukherjee P. Ethical and Regulatory Consideration for Surgeons as Consumers and Creators of 3D Printed Medical Devices. ANZ Journal of Surgery https://doi.org/10.1111/ans.15871

9:Lee MF, Steffens D, Chung J, Posniak S, Cheng K, Clark J, Wallace G, Mukherjee P. Cells Tissue Organs. Co-culture of chondrocytes and stem cells: a review of head and neck cell lines for cartilage regeneration. 2024doi: 10.1159/000538461. PubMed PMID: 38513621

10: Cheng, K.; Curthoys, I.; MacDougall, H.; Clark, J.R.; Mukherjee, P. Human Middle Ear Anatomy Based on Micro-Computed Tomography and Reconstruction: An Immersive Virtual Reality Development. Osteology 2023, 3, 61-70.