A Potential Contraindication to Mastoidectomy?

Caso Clínico Seno petrosquamosal: ¿una contraindicación potencial para la mastoidectomía?

Petrosquamosal sinus - a potential contraindication to mastoidectomy?

Ricardo Jorge Pereira Matos, Gil Coutinho, Pedro Marques, Margarida Santos

www.sgorl.org 99 Acta nº13 - 2020 Department of Otorhinolaryngology, Hospitalar de São João, Porto, Portugal.

Department of Surgery and Physiology/Otorhinolaryngology, University of Porto Medical School, Porto, Portugal.

Correspondencia: ricardo.matos898@gmail

Fecha de envío: 17/12/2019 Fecha de aceptación: 29/1/2020

ISSN: 2340-3438

Edita: Sociedad Gallega de Otorrinolaringología

Periodicidad: continuada.

Web: www.sgorl.org/ACTA

Correo electrónico: [email protected] www.sgorl.org 100 Acta nº13 - 2020 Acta Otorrinolaringol. Gallega 2020; 13: 99-108 Resumo

Introdução

O seio petroscamoso (PSS) é um remanescente venoso embrionário, que drena os seios venosos durais para o sistema Venoso Jugular Externo (EJV). Técnicas de imagem recentes permitem a sua identificação, pela observação de canais de grande calibre. Devido ao considerável risco hemorrágico, o PSS persistente pode levar a consequências fatais durante procedimentos cirúrgicos, como a mastoidectomia.

Caso Clínico

Homem de 64 anos apresentou-se no Departamento de Otorrinolaringologia com história de otorreia esquerda, zumbido ipsilateral e perda auditiva bilateral, com evolução de cerca de 2 anos. O exame otos- cópico revelou colesteatoma atical esquerdo. A tomografia computadorizada (TC) de ossos temporais de alta resolução revelou uma densidade de tecidos moles na orelha média, aditus ad antrum, antro e células mastóideas com erosão da cadeia osicular e scutum. Foi também observado um canal de veia emissária proeminente, consistente com um PSS persistente.

Por esse motivo, optou-se pela não realização de uma mastoidectomia para a erradicação da doença, uma vez que o risco de lesão vascular poderia superar os benefícios cirúrgicos. Depois de alcançar um ouvido seco, foi adotada uma estratégia expectante de vigilância.

Conclusão

O diagnóstico por imagem de um PSS persistente, como uma possível variante anatómica do osso temporal, é de grande importância, pois pode mostrar o local e o curso da veia, prevenindo riscos potenciais durante a mastoidectomia ou, inclusive, contra-indicando a cirurgia.

Palavras-chave

Seio petroscamoso; anatomia do osso temporal; mastoidectomia

www.sgorl.org 101 Acta nº13 - 2020 Acta Otorrinolaringol. Gallega 2020; 13: 99-108 Abstract

Introduction

Petrosquamous Sinus (PSS) is an embryonic venous remnant, which drains the dural venous sinuses to the External Jugular Venous (EJV) system. Recent imaging techniques allow its identification, as large channels can be observed. Owing to the considerable haemorrhagic risk, persistent PSS could potentially lead to fatal consequences during surgical procedures, such as mastoidectomy.

Case Report

A 64-year-old man presented at the Otorhinolaryngology Department with an history of intermittent left ear drainage, ipsilateral tinnitus and bilateral hearing loss, with about 2 years of evolution. The otoscopic examination revealed a left attical cholesteatoma. High resolution temporal bone computed tomography (CT) revealed a soft tissue density at the middle ear, aditus, antrum and mastoid cells with scutum and ossicular chain erosions. A prominent emissary vein channel, consistent with a persistent PSS, was addi- tionally observed.

This finding precluded the mastoidectomy for the eradication of the disease, since the risk of vascular lesion could overcome surgical benefits. After achieving a dry ear status, a watchful-waiting strategy was undertaken.

Conclusions

The imaging diagnosis of a persistent PSS, as a possible anatomical variant of the temporal bone, is of paramount importance as it might show the site and the course of the vein, preventing potential risks during mastoidectomy or, even, by precluding surgery.

Keywords

Petrosquamous sinus; temporal bone anatomy; mastoidectomy

www.sgorl.org 102 Acta nº13 - 2020 Acta Otorrinolaringol. Gallega 2020; 13: 99-108 Introduction

Mastoidectomy is one of the most important procedures in middle ear surgery, with a determinant role in the eradication of acute and chronic infectious ear disease1,2.

The knowledge of anatomical variants of temporal bone, particularly of its mastoid and petrous portions, is vital for the performance of otologic surgery1,2. However, it is common for otologic surgeons to neglect the possible existence of remnants or complete posterior fossa emissary veins, with serious implications, from trivial intraoperative bleeding with difficulty in proper disease eradication to fatal haemorrhage and venous ischemia, in those cases in which emissary veins are the major drainage pathway of the posterior fossa2–6.

Petrosquamosal Sinus (PSS) is an embryonic remnant emissary vein, which arises from the posterior and lateral portion of the transverse sinus at its junction with the sigmoid sinus7. Petrosquamosal Sinus connects the dural venous sinuses and the External Jugular Venous System (EJV), through its course over the lateral superior surface of petrous bone and its connection to the pterygoid plexus and retromandibular vein. It is one of the three emissary venous routes described in humans, among posterior condylar vein and mastoid emissary vein, and generally, it involutes during fetal and early postnatal life3.

Anatomical studies have shown that PSS is not a rare finding3. In contrast, the incidence of persistent PSS is quite uncommon in routine Computed Tomography scans, probably due to the small calibre of most PSS, since in the last 3 months of fetal life, emissary veins consist of residual connections between extrac- ranial venous network and intracranial dural venous sinuses6,7.

Recent imaging techniques allow an improved identification of these venous structures, which assume significant clinical importance as they may present considerable haemorrhagic risk during otologic surgery. The injury of the PSS during surgical procedures, such as mastoidectomy, would potentially lead to fatal venous ischaemic and/or haemorrhagic outcomes.

www.sgorl.org 103 Acta nº13 - 2020 Acta Otorrinolaringol. Gallega 2020; 13: 99-108 Case Report

A 64-year-old man presented at our department with complaints of intermittent left ear discharge, ipsilateral tinnitus and bilateral hearing loss, with about 2 years of evolution. Other otological symptoms such as vertigo, otalgia and facial weakness were not present. Otoscopic examination showed a left attical cholesteatoma and normal right otoscopy. The audiogram revealed a moderate bilateral conductive hearing loss. High-resolution Computed Tomography (HRCT) scan of the left temporal bone revealed soft tissue density at the middle ear, aditus, antrum and mastoid cells with scutum and ossicular chain erosions. There was also a prominent mastoid emissary canal (MEV) with an anteroinferior course, extending from the superior part of the sigmoid sinus, following over de lateral superior surface of the petrous bone, inflecting inferiorly until the level of the glenoid cavity plane without connections to temporal veins. This venous course was consistent with a persistent PSS (Fig. 1 and 2). A high jugular bulb with dehiscence for the hypothypanum was also observed (Fig. 3). On the right side, a dehiscence of the posterior arm of the superior semicircular canal was found (Fig.4).

The finding of this large PSS, associated with the occurrence of a MEV on the left side, precluded mastoidectomy for the eradication of the otologic disease, since the risk of vascular lesion could overcome surgical benefits. Therefore, an in-office active surveillance of the left attical cholesteatoma was the approach of choice.

Fig. 1 - a) Axial HRCT temporal bone showing a large mastoid emissary canal (white arrowheads) extending from the superior part of the sigmoid sinus (white arrow), on left side. b) Axial HRCT temporal bone showing the left petrosquamosal canal.

Fig. 2 - a) Coronal HRCT of the left temporal bone showing the large petrosquamosal canal (white arrowhead) at the site where the PSS emerges from the left sigmoid sinus (white arrow). b) Coronal HRCT of the left temporal bone showing petrosquamosal canal along its course on the lateral superior surface of the pertrous bone (white arowhead) and erosion of the scutum (white arrow) and of the ossicular chain, associated with soft tissue density ate the aticus, corresponding to attical cholesteatoma. c) Coronal HRCT of the left temporal bone showing petrosquamosal canal at the level of the glenoid cavity plane (white arrowhead) and the mandi- bular condyle (white arrow). www.sgorl.org 104 Acta nº13 - 2020 Acta Otorrinolaringol. Gallega 2020; 13: 99-108

Fig. 3 - Axial HRCT temporal bone showing a high jugular bulb with dehiscence for the hypothypanum on the left side ( white arrow).

Fig. 4 - Axial HRCT temporal bone showing the anterior arm (white arrow) and the dehiscence of the posterior arm ( black circle) of the superior semicircular canal.

www.sgorl.org 105 Acta nº13 - 2020 Acta Otorrinolaringol. Gallega 2020; 13: 99-108 Discussion

PSS follows an anterior and inferior course along the superior and lateral part of the petrous bone, above the petroescamosal suture of the temporal bone, either in a groove or in a bony canal, the latter with the denomination of temporal canal of Vergi3.

Anatomical studies have shown that PSS is not a rare finding with some authors advocating that PSS sinus remnants are the rule and not the exception3.

However, PSS is quite uncommon in routine Computed Tomography (CT) scans. The first radiological description, reporting the characteristic findings on imaging was made by Marsot-Dupuch et al., in 20017. The incidence of persistent PSS in routine computed tomography (CT) is around 1%, well below the 23% reported by Ruiz et al3,6. Given the proximity of the PSS to the bone and its small caliber, radiological identification is only possible in the presence of a large-caliber PSS or with a path along a bone channel in the petroescamosal suture5.

The main reasons for the persistence of PSS and other emissary veins are, according to the literature, controverse.

In 2001, Marsot-Dupuch et al. stated a correlation between the persistence of emissary veins and the presence of high flow vascular malformations, severe hypoplasia or aplasia of the IJVs, all of which may be associated with craniofacial malformations, such as craniosynostosis7.

However, other studies have shown the persistence of emissary veins in the absence of vascular or skull base malformations3–6.

In addition to developmental reasons for these anomalies in the venous drainage patterns of the posterior fossa, major trauma, mastoiditis, meningitis and venous thrombosis are potential causes of persistence of emissary veins, such as PSS6.

In our case, despite a large persistent PPS on the left, a homolateral high jugular bulb was identified, with no signs of hipoplasia or atresia of the IJV drainage pattern. The presence of a dehiscent posterior arm of the right superior semicircular canal was also found.

The persistence of emissary veins, in particular the PSS arising from a mastoid emissary vein, raises concerns about potential uncontrolled haemorrhage during middle ear surgery, such as in mastoidectomy2,6.

Most haemorrhages are trivial, making it difficult to eradicate the middle ear disease, especially if per- formed by an inexperienced surgeon6. The existence of venous variations of the temporal bone is often neglected. Injury of the PSS may lead to a profuse haemorrhage and consequent fatal venous ischemia, especially in the presence of a large PSS representing the major or the only venous outflow pathway of the posterior fossa2,6. In these situations, a careful surgical approach is of paramount importance, in order to avoid the injury of the remnant venous structure. In some occasions, an adjusted surgical technique is mandatory. A possible alternative approach is endoscopic surgery of the middle ear, without the need for mastoid drilling, which allows an excellent view of the spaces around the corner, especially in cases of cholestetaoma limited to the attic and the middle ear.

www.sgorl.org 106 Acta nº13 - 2020 Acta Otorrinolaringol. Gallega 2020; 13: 99-108 CONCLUSION

The imaging diagnosis of the PSS, as a possible anatomical variation of the temporal bone, is of paramount importance as it may be troublesome during otologic surgical procedures, such as mastoidectomy. Thus, awareness of this vascular variants is fundamental for the otologic surgeon.

CONFLICT OF INTEREST

The authors declare no conflict of interest.

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