Clinical and anatomical perspective of the meningohypophyseal trunk: a comprehensive review.

Introduction
Recently, due to development of microsurgery and neoadjuvant therapy methods of intracranial tumors, interventional procedures involving cavernous sinus area have emerged as accessible management option. The largest vessel localized within the cavernous sinus is the internal carotid artery (ICA) which provides arterial supply to nearby cranial nerves and pituitary gland through its branches namely: meningohypophyseal trunk (MHT) and inferolateral trunk (ILT), superolateral trunk and McConnell’s capsular arteries [1, 12]. Due to small diameter and their anatomical variations, above mentioned vessels are at risk of injury during trancavernous endoscopic procedures [1]. The most important branches from clinical viewpoint are ILT and the MHT. Evidence from literature suggests that branches of both these trunks contribute to arterial supply of skull-base meningiomas [35], arteriovenous malformations (AVM) and dural arteriovenous fistulas (DAVF) [18]. Therefore, the ILT and MHT have emanated as popular access sites for catheterization and preoperative embolization [18, 35]. Three branches arise from MHT: tentorial artery (TA), inferior hypophyseal artery (IHA) and dorsal meningeal artery (DMA). Although considerable anatomical details are available in published literature regarding MHT, its anatomical variations (reported frequently) mandates careful consideration during the catheterization of cavernous part of the ICA. The aim of this study is to summarize available current data regarding morphological attributes of the MHT with subsequent analysis of their impact on the interventional procedure of arterial embolization.

Materials and methods
This review was performed between January and March 2025 according to the PRISMA 2020 guidelines [33]. The search through databases was performed by two experienced authors [JD, VP] on PubMed and Embase using keywords as following ‘meningohypophyseal trunk’, ‘meningohypophyseal’ AND/OR ‘trunk’. Authors also included 1 study through analysis of citations [28]. Inclusion criteria were stated as follows: studies focused on anatomy of the MHT—variants of branching, point of origin from the ICA, measurements of the MHT and studies wherein embolization of the MHT was performed and described – method of embolization and instruments used during procedure. Exclusion criteria were as follows: case report, review article, book chapter, studies written in language other than English, studies with scarce description of the MHT, studies describing embolization procedure on other ICA branches than MHT. The Rayyan software [32] was used by authors [JD, VP] during screening phase to avoid imprecise data retraction of studies which met inclusion criteria basing on a title and abstract. Any duplications were found using abovementioned software and removed. Any conflicts of screening results were discussed and resolved with consensus among the rest of the authors [AM, JD, VP]. The PRISMA 2020 flow diagram shows full process of data retrieval (Fig. 1). Authors extracted the following information from included studies: title, authors’ names, year of publication, study population, morphology of the MHT: complete or incomplete type, origin from the ICA, measurements, method of the MHT embolization with type of microcatheter and embolic agent used, success rate of embolization and any complications after the procedure.

Results
A total of 239 studies were found through databases and 180 of them were duplicates. After removal of duplicated studies, 149 records were screened, and 99 of them were excluded. Out of 50 included studies, 49 were retrieved and their full-texts were analyzed and 25 of them were included to this review (17 studies depicting anatomy of the MHT and 8 studies focused on embolization of the MHT) (Fig. 2).

Anatomy of the MHT
Detailed information about variations of the MHT was found in 10 out of 17 anatomical studies [1, 3, 11, 16, 20, 23, 26, 28, 30, 36]. The MHT was present in almost all of the cases except 3 studies [11, 20, 30], wherein the MHT appeared from 75 to 96%. The most frequent variant of the MHT was complete type—trifurcated into the IHA, TA and DMA (in abovementioned studies it was present from 58.3 to 96% of cases). From incomplete types of the MHT the most commonly seen type was bifurcation into TA and DMA with IHA arising directly from the ICA or absent. Some most frequent variants of the MHT are presented in Fig. 3. The tentorial artery was the most constant branch of the MHT – in 6 out of 10 studies was seen in all of analyzed MHTs [1, 16, 23, 28, 30, 36]. Detailed data of anatomical variations of the MHT was summarized in Table 1. All included anatomical studies [1, 3, 9, 10, 11, 16, 20, 21, 23, 26, 28, 30, 31, 34, 36, 41, 42] reported parts of the ICA wherein the MHT originated (Fig. 2). The most common origin of the MHT was posterior loop of the cavernous part (C4 according to Bouthillier classification of the ICA—79,56% of all analyzed cases). Less common origin of the MHT was C3 part and horizontal fragment of the C4 (12,68% and 7,76% respectively).

Embolization of the MHT
We identified 6 out of 8 included studies, wherein there were cases with performed embolization of the MHT only [15, 17, 18, 37, 40, 43]. Successful embolization was achieved in almost all of the patients, except one study [43] wherein 73.7% had successfully embolized vessels. The most common group of cases was represented by patients with intracranial tumors, majority of them were meningiomas. Other groups of cases included: arteriovenous malformations and 1 case of dural arteriovenous fistula. In 3 articles authors reported complications after embolization: palsy of cranial nerves and in 1 case embolic stroke [15, 18, 40]. Summary of these cases is presented in Table 2.

Due to proximity between the ILT and the MHT, many cases of intracranial tumors have arterial supply from both these vessels. Therefore, some studies analyzed results of embolization of both the ILT and MHT [13, 35]. Some of studies presented in Table 2 reported also cases of combined embolization of the ILT and MHT [15, 18, 37]. Summary of ILT + MHT embolization methods and results was presented in Table 3.

Measurements of the MHT
Three out of 17 included anatomical studies described diameter of the MHT [9, 28, 41] which is usually smaller than 0.5 mm (approximately from 0.1 to 0.3 mm according to Ćetković et al. (2020) [9] and Tran-Dinh 1987 [41]). McConnell reported diameter 0.75 mm [28]. According to 2 authors [28, 41] MHT branching off occurs after 1–3 mm of its course. In relation to the foramen lacerum 2 studies reported distance varying between 5.3 and 15.7 mm [1, 3]. Localization of the MHT in relation to the sellar floor was analyzed in one study and mean distances were 8.9 mm anterior and 3.8 mm superior to the sellar floor [1].

Discussion
Discovery of the meningohypophyseal trunk is associated with exploring the arterial supply of pituitary gland which comprises of superior and inferior hypophyseal arteries. The inferior hypophyseal (IHA) supplying neurohypophysis was at first described by Luschka in 1860 [25]. Subsequent research findings as elaborated by McConnell [28] shows that IHA in most cases originates not directly from ICA but as one of the three branches arising from common trunk (MPT) with the morphological details varying between individuals [28]. These three branches were depicted as anterior, posterior and inferior hypophyseal arteries based on their course in relation to pituitary gland. According to its course the anterior branch corresponds to the tentorial artery (or marginal tentorial artery) also known as the artery of Bernasconi and Cassinari who identified this vessel as an important feeder of the tentorial meningiomas and assumed that its presence might be pathognomonic for these kind of tumors in tentorial area [6]. The posterior branch as described by McConnell (1953) [28] corresponded to the dorsal meningeal (or dorsal clival) artery (DMA) which supplies Dorello’s canal—a critical structure in microsurgical procedures [27]. The DMA usually anastomose with a contralateral counterpart and sometimes also with a branch of the external carotid artery (ECA) – the ascending pharyngeal artery [29, 31] via the neuromeningeal trunk [14]. Another analysis related to the trunk (origin of the three hypophyseal arteries) was made by Parkinson [34] who named it as ‘meningohypophyseal artery or trunk’ with description of all its branches and variations [34]. Harris and Rhoton (1976) [16] also mentioned about a sporadic branch from the MHT arising mostly from the ICA and is referred to as ‘artery of the inferior cavernous sinus’ in the literature according to description of its course. However, the above artery may also be a variant of one of the branches of the inferolateral trunk (ILT) [20].
It is noteworthy that more than 20% of skull base meningiomas receive their blood supply from the ECA, mostly through anastomoses with the ICA [2]. The aforementioned anastomoses usually have a small diameter and are therefore often undetected during radiologic examinations. The prevalence of external carotid–internal carotid anastomoses varies depending on whether the evaluation is performed using in vivo or cadaver angiography. Middle meningeal artery is another important feeder of skull base meningiomas and might form anastomoses with branches of the ICA, most commonly with the lacrimal artery. Analysis of meningolacrimal anastomosis prevalence using angiography in cadaver specimens has revealed a significantly higher frequency of these anastomoses compared to in vivo examinations, likely due to the absence of physiological blood flow, which affects diagnostic accuracy [38]. Therefore, there remains a need to expand knowledge about other anastomotic channels between the ECA and ICA through the application of both in vivo and cadaver methods. Also, analysis of embryological development of carotid arteries might help better understanding the origin of EC-ICA anastomoses [22].
Structures supplied by branches from the MHT are mostly documented in literature in the following form: tentorium and clival area, neurohypophysis, third, fourth and sixth cranial nerves. The Gasserian ganglion which has its arterial supply mostly from the ILT might also receive some branches from the tentorial artery [23, 31]. Arterial supply provided by MHT to the structures as mentioned above emphasizes the importance of careful assessment of its branches during surgeries involving clival and cavernous areas.
Bernasconi’s and Cassinari’s angiographic research involving of tentorial meningiomas catalyzed search of microcatheterization methods such as embolization of tumor feeders [3]. Preoperative embolization of intracranial tumors is a well-known neoadjuvant therapy which reduces tumor mass and facilitates subsequent resection. The most common type of tumor supplied by MHT as observed in the present study was meningioma. Although, most of the skull base meningiomas are supplied by both ECA and ICA catheterization of the ICA branches is more challenging due to their small diameter and tortuous course which increases risk of embolysate reflux. Preoperative embolization of tumor feeder artery in selected cases might facilitate chance of total tumor resection, however, for intracranial ICA branches the exercise is associated with substantial risk of complications. About 20% of meningiomas are supplied by MHT [19] and it is noteworthy that the short anatomical course of MHT as well as ILT are associated with high risk of reflux during embolization. This aspect renders the invasive procedure a challenging one [35, 43]. There are some sporadic complications after embolization of the MHT such as thrombosis, cranial nerve palsy or carotid-cavernous fistulas [4, 18, 40] and embolic infarction as a result of the reflux [18, 35]. However, thorough preparation before the procedure allows for considerable decrease in risk of complications as mentioned above. Therefore, better understanding of the MHT morphology, various embolization methods and proper selection of embolic material might be helpful to achieve positive outcomes in patients [35].
There are various embolization techniques developed to improve safety of neoadjuvant therapy of skull base tumors. Hirano et al. [18] presented a novel technique of shaping microcatheter individually to the patient’s ICA with a tip sealing the orifice of the side branch thus lowering the risk of embolic reflux into the ICA. However, it may be considered that this method was associated with transient cranial nerve palsy in some patients [18]. Distal balloon protection technique as proposed by Yamashiro et al. [43] may also address the problem of the embolic reflux from the MHT and ILT by occluding the ICA with the balloon at the point of ophthalmic artery bifurcation to avoid migration of embolic particles during the injection process [43]. According to observations made in present study, use of balloon protection technique entailed lower risk of complications (Tables 2 and 3). Preoperative embolization of intracranial tumors through innovative techniques (as reported in literature) not only increases chance of total tumor resection, but also potentially reduce risk of pituitary apoplexy after removal of pituitary adenoma [13].
Most commonly used embolic agents as observed in this study were polyvinyl alcohol (PVA) and n-butyl cyanoacrylate (NBCA). PVA is broadly known as particulate embolization agent which provides permanent occlusion with possibility of re-embolization if needed. It may be noted that PVA particles may vary in in size, which sometimes might cause blockage of catheter. Also, it is to be considered that with PVA the level of embolization is difficult to estimate. Cyanoacrylates on the other hand, are low-priced liquids which offer rapid occlusion but require some level of expertise in application of the same [24]. However, they have higher risk of embolysate reflux and can also enter small-sized anastomoses with ECA, which are often not visualized on angiography. Using PVA with larger particles (>150 μm) may minimize the risk of occluding small anastomotic channels and thereby reduce the likelihood of potential complications [14]. Notably, there is no significant correlation between use of any specific agent and successful embolization of skull-base meningiomas as reported in literature [8]. Moreover, choice of any particular embolic agent during preoperative embolization may rather be adjusted to subjective preferences of the observer for optimum clinical outcome [5].
Barros et al. [5] identified predictors of complete endovascular embolization of meningiomas and accordingly the most significant predictors involved arterial supply by ascending pharyngeal artery and presence of convexity or parasagittal meningioma. Arterial supply by the MHT is also reported was found to be a significant predictor for preoperative partial or complete embolization [5] what renders this arterial trunk an important target for neoadjuvant therapy involving skull base meningiomas. None of the authors of included clinical studies specified variants of the embolized MHTs, therefore we cannot predict which anatomical variant of this vessel has prominently higher risk of possible complications.
Detailed anatomical knowledge about small arteries nearby the cavernous sinus is essential from clinical viewpoint during endonasal endoscopic procedures. During transcavernous endoscopic approach in most of the cases the MHT is the first branch that surgeons come across about 4 mm above the floor of sella turcica with the MTA (branch of the MHT constantly present) observed in superior part of the cavernous sinus and the DMA in its posterior part [1, 12]. Notably, the ILT is usually localized in lateral and inferior compartments of the sinus [1].
Due to clinical importance of the MHT, there is still need to investigate anatomical variation of this structure and the other. During teaching, academics should make students aware of variability of the human anatomy [39].

Conclusions
Information about anatomy of the MHT might be helpful during planning endoscopic procedures involving cavernous sinus and embolization. Although, in most cases the morphological details of MHT aligns with standard descriptions, however, some anatomical variations of its branches should be considered. According to our results we cannot determine which anatomical variant of the MHT is associated with higher risk of complications during the embolization procedure which probably in majority of cases depends on subjective choice of embolization method. Balloon protection during embolization might decrease occurrence of complications as risk of embolic reflux during embolization of the ICA branches (MHT and ILT) is on the higher side. From a broad perspective, method of microcatheterization or choice of embolic agent should be approached with a customized perspective based on experience and preference of operator to avoid possible complications such as cranial nerve palsy. There is still a need to expand knowledge about the impact of particular anatomical variants of the MHT on embolization efficacy and safety.