7 Skin Incisions, Head and Neck Soft-Tissue Dissection An adequate planning of skin incision and selected flaps are essential in Neurosurgery. In order to do that, it is important to keep in mind the vascular pedicles of the scalp from the cervical region to the orbit. We also must consider the distribution of nerves, as well as muscle fascias and muscle insertions. Ideally, all incisions should be hidden behind the hairline for cosmetic reasons. Since specific cutaneous flaps could be performed through different myofascial and muscle incisions, the overall standard should consider flaps with a wide support, respecting a vascular-nervous axis in order to guarantee its functional preservation. This peculiarity optimizes flap viability, thus avoiding possible functional and/or aesthetic sequelae. In this chapter, we will analyze head and neck soft-tissue structures, including vascular-nervous patterns, establishing the precise location for incisions and flaps used in Neurosurgery. Head and neck soft-tissue structures consist of the following layers • Skin (epidermis and dermis). • Subcutaneous fibro-adipose tissue or superficial muscleaponeurotic system (and facial muscles). • Epicranial aponeurosis or galea. • Temporal or deep fascia (including superficial and deep layers). • Muscles. • Periosteum. • Longitudinal incisions (Fig. 7.1) ◦ Midline-suboccipital incision (Fig. 7.1A). ◦ Retromastoid (retrosigmoid) incision (Fig. 7.1B). ◦ Temporal incision (Fig. 7.1C). • L and/or S-shaped incisions (Fig. 7.1) Applied for: ◦ Inter-hemispheric approaches: A sagittal incision is followed by a limb orientated towards the lesion side (Fig. 7.1D). ◦ Unilateral posterior fossa approaches: A midline suboccipital incision is followed by a limb starting from the Inion, and running along the superior nuchal line to the mastoid process (Fig. 7.1E), also known as “hockey stick incision.” When L-shaped incisions are not sufficient for surgical exposure, S-shaped incisions might be considered; they are performed by extending the incision with an additional opposed limb to allow a wider exposure (Fig. 7.1D). Some surgeons also prefer a lazy S-shaped incision to those with very sharp turns, especially on the convexity for superior healing and reduced risk of infections. Fig. 7.1 Longitudinal incisions. (A) Midline-suboccipital incision: caudal to the inion. (B) Retromastoid (retrosigmoid) incision: longitudinal vertical incision at the level of the lateral third of the line joining the inion and the mastoid tip. (C) Temporal incision: vertical incision from the zygomatic arch (1 cm anterior to the tragus) and extended as needed. (D) Longitudinal incision with a lateral limb and/or S-shaped incision (longitudinal incision with two opposite limbs). (E) Midline suboccipital incision followed by a limb from the inion along the superior nuchal line to the mastoid process also known as “hockey stick incision.” (F) Combined post-auricular C-shaped incision oriented to skull base approaches, from the margin of the sternocleidomastoid muscle to the superior temporal line in most cases. This incision can be combined with others to extend the approach to the anterior and middle cranial fossa, so it is important to preserve the vascularity of both anterior and posterior flaps. • C-shaped incisions or cutaneous flaps (Fig. 7.2) ◦ Fronto-temporal (Fig. 7.2A) ◦ Bicoronal (Fig. 7.2B) ◦ Temporal (Fig. 7.2C) ◦ Parietal (Fig. 7.2D) ◦ Occipital (Fig. 7.2E) ◦ Horseshoe incision (Fig. 7.2F) In surgical anatomy, the dissection techniques and approaches have to be planned thoroughly, in order to obtain a successful reconstruction and prevent possible complications. The general planning should include ◦ Sufficiently wide incisions and cutaneous flaps. ◦ Avoidance of excessive edge tractions. ◦ Care to preserve myofascial and pericranial structures integrity. The subgaleal layer is very important for several reasons. This virtual space is almost avascular, easily detachable, resistant to self-retaining retractors, and protects the related vascular-nervous pedicles. By means of subgaleal detachments we can obtain extensive layers of pericranium (see Chapter 6). This is of great relevance as the replacement of the dura mater, since this may have to be removed in several instances. Furthermore, it is very useful both for sinuses occlusion in frontal exposures before dural opening and skull base approaches. Several vascular pedicles, originating from the external carotid artery, reach the scalp. They establish anastomosis among each other and with the opposite side. • Anterior group ◦ Supraorbital pedicle (supraorbital artery and lateral branch of supraorbital nerve). ◦ Medial-frontal pedicle (supratrochlear artery branches and medial branch of supraorbital nerve). • Lateral group ◦ Temporal pedicle (superficial temporal artery and auriculo-temporal nerve). ◦ Mastoid pedicle (posterior auricular artery and lesser occipital nerve). • Posterior group ◦ Occipital pedicle (occipital artery, greater occipital nerve and medial branch of the third cervical dorsal nerve). • Cervical plexus (in particular, the great auricular nerve). • Facial nerve (VII cranial nerve): mandibular branch. • Spinal accessory nerve. • Carotid sheath. • Vertebral artery and glossopharyngeal (IX), vagus (X) and hypoglossal (XII) cranial nerves. • At the frontal level, in case of orbital exposure, the periosteum must be detached reaching the supraorbital notch (Fig. 7.3) (see Chapter 6). • At the temporal level, just above the zygomatic arch, the superficial temporal artery appears subcutaneously. The temporal and frontal branches of the facial nerve run superficial to the zygomatic arch, at about 2 cm from the tragus, and run parallel and anterior to the superficial temporal artery (Fig. 7.4). Therefore, the incision must preserve the frontal branch of the facial nerve, by sectioning the superficial layer of deep temporal fascia, avoiding undesirable eyebrow asymmetry. Immediately after this step, the temporal muscle is detached leaving a cuff of muscle for further reconstruction (Fig. 7.5). • At occipital level (Figs. 7.6, 7.7) attention should be paid to the occipital artery and greater occipital nerve. Its injury may lead to a sensitive alteration or neuralgic pain at the ipsilateral occipital region. Artery and nerve are located about 3 cm lateral to the inion, between trapezius muscle fibers.
7.1 Introduction
7.2 Soft-Tissue Structures
7.3 Cutaneous Cranial Incisions
Abbreviations: I = inion; L = longitudinal incision; M = mastoid; RSI = retrosigmoid incision; S = S-shaped incision; SNL = superior nuchal line; TI = temporal incision.
7.4 Cranial Vascular-Nervous Axes
7.4.1 Classification
7.5 Vascular-Nervous Structures of the Neck
7.6 Flaps and Vascular-Nervous Axes
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