Reconstruction of the anterior skull base with free muscle flap after iatrogenic injury

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The anterior skull base is an important bar­rier between the sinonasal tract and intracranial space [1]. After major neurosurgical re­sec­tions, traumas or even iatrogenic injury, it is neces­sary to meticulously close the defect in the skull base. Otherwise, the defect can cause meningitis, epidural absces­s, leakage of cerebrospinal fluid (CSF) or even death [2]. The primary goal is to separate the non-sterile space of the nasal cavity and sterile extradural space. It is also neces­sary to support the brain and orbit, to reestablish the nasal cavities, to provide volume to decrease dead space and to restore the appearance of the face [3]. There are several techniques for skull base defect closure. In case of small defects, local flaps such as the temporalis muscle are often used. If the defect is larger or infected, distant flaps such as the latis­simus dorsi or trapezius muscle should be used. Even better results cover­­ing large defects are obtained us­­ing free flaps like the rectus abdominis muscle [4,5]. Free flaps have many advantages; they can fill the dead space, cover large defects and provide a wel­l-vascularized environment and stable bar­rier between the nasopharynx and extradural space [6]. The skull base reconstructions are, however, technical­ly dif­ficult and their failure can cause life-threaten­­ing complications.

We report on a 70-year-old patient who suf­fered from chronic osteomyelitis of the frontal bone fol­low­­ing trauma. He underwent a com­mon nasal polypectomy and shortly after the procedure, he developed nasal liquor­rhea from the right nostril. CT images showed a pneumocephalus and a defect in the right part of the ethmoidal bone (Fig. 1). First, the ear, nose and throat (ENT) surgeon indicated closure of the defect with a nasoseptal flap, which showed no ef­fect. A team consist­­ing of a maxil­lar surgeon, neurosurgeon and ENT surgeon tried to close the defect of the rhinobasis us­­ing the pericranial flap for cranialization of the frontal sinus. After the procedure the liquor­rhea stopped; however, 2 weeks after the operation the patient’s state deteriorated. He started to be septic with purulent meningitis. PET-CT showed no infectious focus, but repeated nasal endoscopy showed a purulent slime mas­s. The smears from the rhinobasis and hemoculture examination confirmed the extended-spectrum beta-lactamase produc­­ing Klebsiel­la pneumonie and coagulase negative Staphylococcus. Repeated CT and MRI showed no intracranial infectious complication and good cranio-nasal separation. However, the patient was septic, he developed a heavy psychoorganic syndrome and he needed vasopres­sor ther­apy with norepinephrine. After repeated nasal endoscopy and debridement, the defect in the rhinobasis reoccur­red. Therefore, a team of physicians came up with the last pos­sible solution –  closure of the rhinobasis defect with a free muscle flap.

For the reconstruction, we decided to use the left rectus abdominis muscle. Two teams operated on the patient. The first team raised the free muscle flap from a paramedian incision, dis­sected the inferior epigastric artery and vein and closed the donor site primarily. The second team operated on the head from the old bicoronal incision. We transfer­red the flap to the defect in the rhinobasis. The flap separated the nasopharynx from the anterior cranial base. We sutured the pedicle ves­sels to the right superficial temporal artery and vein (Fig. 2A).

In the early postoperative period, there was a slight left-sided hemiparesis and minor swel­l­­ing of the frontal lobes, which was caused by the pres­sure of the flap and frontal bone. However, both problems subsided gradual­ly. There were no complications related to the flap or donor site. We checked the anastomosis patency via hand Doppler US and CTA. After the operation, the patient showed no sign of liquor­rhea, pneumocephalus or infection (Fig. 2B). After 20 days, the skin suture was completely healed.

The patient did not need any other ope­ration since then and the anastomosis was patent at the 1-year fol­low-up.

Cranial base reconstruction is a life-sav­­ing procedure. In the past two decades, several techniques have been developed. Local flaps such as the temporalis muscle represent a good choice for reconstruction, when the defect is small and the soft tis­sue requirement is minimal [7]. Free muscle flaps like the rectus abdominis muscle or anterolateral thigh are an excel­lent choice for cover­­ing larger defects, since they can easily obliterate dead space; they are suitable for people who underwent radiation ther­apy and they provide a wel­l-vascularized environment, which is neces­sary for deal­­ing with infection and for proper healing [5]. For the closure of the defect of the rhinobasis of our patient, we used the free rectus abdominis muscle. Beside our preference, this free flap has a long vascular pedicle with a large diameter, which provides vascular anastomosis outside of the skul­l. The dis­section of this flap is relatively easy and thanks to its localization, it is pos­sible for two teams to work on it simultaneously [8]. With regard to complications at the donor site, there is the pos­sibility of lower abdominal wall weaknes­s [9]. Risk of these complications is minimal when we harvest a unilateral flap. It is also pos­sible to use a fascia lata free flap, which also has a long pedicle and its donor-site morbidity is very low due to a lack of tension. More com­mon free flaps are the latis­simus dorsi muscle and gracilis muscle. Latis­simus dorsi muscle flap can cover large defects; however, two teams can­not work on it simultaneously. Gracilis flap is suitable for harvest­­ing at the same time while the other surgical team operates on the head; conversely, it has a short vascular pedicle and smal­ler volume [5]. Compar­­ing local and free flaps, local flaps have lower morbidity at the donor site, easier surgical transfer and shorter operat­­ing time. Free flaps are, however, highly resistant to infection, provide a wel­l-vascularized environment and suf­ficiently cover bone defects, so it is not neces­sary to use bone grafts. Cranial base reconstruction procedure was perfected dur­­ing the past few years, mainly due to improvements in microvascular technique, endoscopic equipment and image guidance. However, it is still a very risky operation with many pos­sible complications. The most com­mon ones are CSF fistula, infection, pneumocephalus and free flap pedicle ves­sel thrombosis.

The skull base defect is a serious con­dition, which demands wel­l-plan­ned surgery with multidisciplinary cooperation among the ENT surgeon, neurosurgeon and plastic surgeon along with a very good knowledge of the anatomy of the skull base.

The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study.

The Editorial Board declares that the manu script met the ICMJE “uniform requirements” for biomedical papers.

Accepted for review: 23. 5. 2018

Accepted for print: 29. 8. 2018

Matěj Patzelt, MD

Department of Plastic Surgery

Third Faculty of Medicine

Charles University

Šrobárova 1150/50

100 34 Prague

Czech Republic

e-mail: matej.patzelt@centrum.cz