7 Transcribriform Approach

The transcribriform approach is most frequently employed to resect tumors of the anterior skull base via a transnasal endoscopic route. Formally, the term “transcribriform approach” is anatomically inaccurate as it refers only to the cribriform plate, while almost invariably resection also includes the ethmoidal roof (or fovea ethmoidalis). ^{1 , 2} During the last decades, this corridor progressively became the mainstay for the surgical management of a wide array of diseases involving the anterior skull base, including meningiomas, ³ – ⁷ schwannomas, ^{8 , 9} dysembryogenic lesions, ¹⁰ sinonasal malignancies, ¹¹ – ²² and other tumors or tumorlike lesions. ¹ On the other hand, its indications in the management of some tumors of the anterior skull base (i.e., meningiomas of the cribriform plate and/or ethmoidal roof) are controversial and factors like the status of olfaction before surgery and the possibility of its preservation should be considered in the decision-making process. ^{23 , 24 , 25} Moreover, the anatomy of the transcribriform approach should also be mastered when treating cerebrospinal fluid leaks of the cribriform plate or ethmoidal roof, though, in such circumstances, the resection of sinonasal structures is commonly less extensive. ^{26 , 27}

The transcribriform route is limited anteriorly by the bony angle joining the posterior frontal plate with midline anterior skull base, posteriorly by the ethmoidal–sphenoidal junction and laterally by the medial orbital walls. To get access to the anterior skull base through the nose, the ethmoidal box must be disassembled according to the needs of resection and exposure. The most extensive variant of this approach, which includes a binostril corridor with a subtotal septectomy, is detailed in the present chapter. Subtotal septectomy is performed for oncologic reasons because most nasal–ethmoidal lesions directly invade the septum and/or with the intent to provide a binostril access to the surgical field with the advantage to work with a four-hand technique. This approach offers to the surgeon a wide and sequential view of the skull base layers that are invaded by tumors arising from nasal–ethmoidal complex, thus allowing for a tailored and targeted resection. However, it is worth mentioning that a unilateral transcribriform approach gives the patient the possibility to maintain at least partially the sense of smell, as demonstrated by recent studies on the surgical treatment of unilateral tumors without septal extension. ²⁸ With a similar philosophy, spontaneous or post-traumatic/-surgical cerebrospinal fluid leaks and/or meningoencephaloceles are usually managed with conservative variants of the transcribriform approach herein presented, with the aim to minimize postsurgical morbidity. As an additional remark, the transcribriform corridor provides a direct view of the gyrus rectus and medial orbital gyrus, whose minimal invasion can be managed with endoscopic subpial dissection without the need for craniotomy.

The transcribriform approach crosses by its nature the course of ethmoidal arteries, whose variable anatomy must be fully understood to coagulate and cut them safely, minimizing the risk for orbital complications. In addition, when the intradural space is entered, the medial orbitofrontal arteries and veins are encountered; their careful manipulation avoids the risk of intracranial hemorrhage, which might be difficult to manage via a transnasal endoscopic approach.

The bony borders of the craniectomy performed while harvesting the transcribriform pathway are usually thick and well defined. As a consequence, they are particularly suitable for multilayered reconstruction with several grafts and flaps that can be variably positioned with respect to the dura mater and bony edges of the skull base. Despite the unquestionable efficacy of vascularized local flaps, ^{21 , 29} they are frequently not available after a transcribriform approach as a consequence of nasal–ethmoidal tumors propensity to invade the nasal septum and turbinates. However, a three-layered reconstruction with fascial grafts (such as the iliotibial tract) demonstrated to be a safe and effective technique that is feasible in almost all cases. ^{30 , 31}

The reader is encouraged to pay particular attention to learn the transcribriform approach as it represents one of the most important steps in the tool kit of endoscopic skull base surgeons.

Related posts:

1 Classification of Endoscopic Transnasal Approaches to the Skull Base and Adjacent Areas 9 Transsellar Approach 17 Medial Transcavernous Approach 15 Transpterygomaxillary Approach 18 Lateral Transcavernous Approach 21 The Suprapetrous (Meckel’s Cave) Approach

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