Introduction

The temporoparietal fascia (TPF) lies under the skin and subcutaneous tissue over the temporal fossa. It is also known as the superficial temporal fascia. It is continuous with the superficial musculoaponeurotic system that is inferior to the zygomatic arch. These two structures are continuous with the platysma muscle in the neck, creating a unified fascia layer from the scalp to the clavicle. The temporoparietal fascia joins the orbicularis oculi and frontalis muscles anteriorly and the occipitalis muscle posteriorly.[1][2][3] It is approximately 2 to 3 mm thick. The layers from the skin to the cranium from superficial to deep in this region are as follows:

• Skin
• Subcutaneous tissue 
• Temporoparietal fascia (superficial temporal fascia)
• Innominate fascia 
• Deep temporal fascia (divides into a deep and superficial layer)
• Temporalis muscle 
• Pericranium
• Cranium 

The deep temporal fascia splits into a deep and superficial layer before it inserts into the superior aspect of the zygomatic arch. The superficial temporal fat pad divides these two layers. A proper understanding of the anatomy surrounding the temporoparietal fascia is essential for surgical considerations as it can serve as donor tissue for reconstruction. Additionally, a thorough knowledge of the temporoparietal fascia's relation to surrounding neurovascular structures is integral to safe surgical dissections in this area.

Structure and Function

Beneath the TPF is a loose areolar and avascular plane separating the TPF from the deep temporal fascia. This layer may be referred to as the innominate fascia. It is this plane of tissue that permits the superficial scalp to move freely over the deeper muscular fascial layers. The combination of the superficial loose layers and the deep tight layers allows the scalp to maintain structural integrity with necessary mobility. Additionally, the role of fascia within the human body is to enclose structures (i.e., muscles, viscera, or neurovascular bundles) into discrete organizational patterns.[4]

Embryology

The development of head and neck structures centers on the branchial and pharyngeal apparatus. At 4 to 7 weeks gestation, the head and neck consist of 5 or 6 pairs of branchial arches. The division of branchial arches is by external indentations called branchial clefts, which are lined by ectoderm. The corresponding inward groove is a pharyngeal pouch that is lined by endoderm. The pharyngeal pouch is the primitive pharynx. Branchial arches are composed of mesoderm. Within the branchial arch mesoderm, connective tissue (i.e., cartilage and fascia) will form.

Blood Supply and Lymphatics

The scalp is rich in arterial anastomoses, with the majority of the blood supply arising from the external carotid artery. The vascular supply to the temporoparietal fascia is the superficial temporal artery, which is the terminal branch of the external carotid artery. It pierces through the substance of the parotid gland anterior to the tragus. The scalp lymphatic system lacks lymph nodes and drains primarily into parotid, anterior/posterior auricular, and occipital lymph nodes. Venous drainage patterns follow that of lymphatic drainage.[5][6]

Nerves

The superficial temporal artery runs within the temporoparietal fascia along with the frontal branch of the facial nerve. The sensory supply to the scalp is from the trigeminal nerve medially and the temporal, auricular, and occipital nerves laterally and posteriorly. Surgical considerations need to account for the course of the frontotemporal branch of the facial nerve in this region. The nerve exits the parotid gland within the parotid-masseteric fascia and will run superiorly within the innominate fascia over the zygomatic arch. At 1.5 to 3 cm above the superior border of the zygomatic arch and 0.9 to 1.4 posterior to the lateral orbital rim, the nerve will transition to a more superficial plane at the undersurface of the TPF. This name for this area is the fascial transition zone.

Muscles

The main muscle occupying the temporal fossa is the temporalis muscle. It is a triangular muscle that broadly originates on the parietal and frontal bone of the temporal fossa and the deep surface of the deep temporal fascia. It attaches to the coronoid process and anterior ramus of the mandible. The trigeminal nerve innervates it via the deep temporal nerves. The action of this muscle is upon the mandible and results in elevation for jaw closure and also causes retraction of the jaw.

Surgical Considerations

The TPF flap provides a wide range of utility in reconstruction within the head and neck. It was first described in 1898 for the reconstruction of an ear (following a horse bite) and reconstruction of the lower eyelid. The advantages provided by the flap are its size and flexibility. Up to 14 cm TPF can be harvested safely, and the flap can act as a fascial, fasciocutaneous, or osseofascial flap. Uses for the TPF are diverse and include forehead/brow, auricular, and lip reconstruction. Additionally, TPF plication can decrease lateral canthal rhytids and elevate the lateral brow during rhytidectomy. Plication also provides deep tissue support and can aid in preventing alopecia and visible scar formation.

When operating in this area, care is necessary to avoid injury to branches of the facial nerve. Dissection in the temporal region is safe above the superficial layer of the deep temporal fascia below the innominate fascia. This approach will ensure that the frontotemporal branch of the facial nerve is superficial to the plane of dissection. Additionally, dissection within the correct plane is necessary for the safe execution of zygomatic arch fracture reduction utilizing the Gilles approach. During this procedure, a 2.5 cm temporal incision is made superior and anterior to the helix within the hairline. Care is necessary to avoid the superficial temporal artery. Dissection continues down to the deep layer of the deep temporal fascia. The fascia is incised, and the temporalis muscle is exposed. An instrument then bluntly dissects between the deep temporalis fascia and the temporalis muscle using a sweeping motion. Once to the level of the depressed zygomatic arch fracture, a Rowe zygomatic elevator is then used to apply an outward force on the fracture.

Additionally, the temporalis fascia has been used routinely in a tympanoplasty for the reconstruction of the tympanic membrane. Given the ease of grafting, this autologous donor site has uses for both medial and lateral tympanoplasty. Temporalis fascia is useful for both subtotal and total repair of tympanic membrane perforations.[7][8][9]

Clinical Significance

As mentioned earlier, a proper understanding of the TPF and its surrounding structures are essential to safely operating in this area. Additionally, understanding fascia layers can help understand the spread of infections and tumors within an anatomical area.

Other Issues

The temporoparietal fascia is a very reliable flap with a good blood supply. However, any injury to the blood supply can easily lead to flap necrosis. In patients with burns, head trauma, or prior surgery to the scalp or skull, the blood supply may suffer compromise - hence its use as a flap is not recommended. One of the ways to assess the blood supply is with the use of Doppler.[10]