Basal vein of Rosenthal anomaly of the telencephalic segment with separate drainage in the deep and superficial middle cerebral veins

Dear Editor, We present the case of a 22 years old male with an uneventful medical history who underwent brain magnetic resonance imaging (MRI) as part of a diagnostic workup for headache. The MRI was unremarkable regarding headaches but revealed an incidental anomaly of the right basal vein of Rosenthal (BVR), characterized by a substantial absence of the first (telencephalic) segment, due to the presence of two separate efferent channels joining at the diencephalic segment [Figures 1-3]. The channels are separated; one is medial and connected to the ipsilateral cavernous sinus (CS), corresponding to the deep middle cerebral vein (DMCV), while the other corresponds to an anastomotic vein connecting the uncal vein (UV) and the superficial middle cerebral vein (SMCV). An UV draining into the DMCV was not identified, but the course of the lateral venous channel partially corresponds to the UV in its medial portion and to the SMCV in its lateral portion. The postcontrast T1-weighted MRI reconstruction in the sagittal plane with maximum intensity projections/multiplanar reconstruction (MIP/MPR) shows the two separate venous channels replacing the telencephalic segment of the BVR on the right side and a normal pattern on the left side [Figures 4 and 5]. The channels are also distinguished in the axial plane at different levels [Figure 6] and in the oblique axial plane [Figure 7], illustrating the difference between the two sides. The drainage pattern on the right side leads to the VoG and the CS through both median and lateral channels, respectively. The drainage of the SMCV extends to the superficial Sylvian vein and the lateral sinus and to the CS via the sphenoparietal sinus [Figures 8 and 9]. The described patterns are not usual, but they cannot be interpreted as pathological, and they were incidentally discovered. Then, MR angiographic sequences were not performed. However, both susceptibility weighted imaging (SWI) and postcontrast turbo field echo T1-weighted sequences demonstrated effective venographic capabilities, with results illustrated accordingly. In addition, a multiplanar reconstruction protocol was applied to both sequences, enabling a thorough examination of the complex venous pathways.Figure 1: Susceptibility weighted imaging magnetic resonance with minimum intensity projections/multiplanar reconstruction protocol in the axial plane focused on the basal vein of Rosenthal (BVR) course. (a) On the left side, is imaged the normal adult pattern of the BVR, with a short telencephalic segment stemming from the joining of the anterior cerebral vein and the deep middle cerebral vein (DMCV). On the right side, this segment is not visible and two different and separated venous channels are shown: a medial one, corresponding to the DMCV (black *) and a lateral one (black >), sharing the course of the uncal vein in its medial portion and the course of the superficial middle cerebral vein in its lateral portion. These venous channels join at the mid-portion of the diencephalic segment. (b) With a slight inferior obliquity, the different course of the posterior cerebral artery (red >) and the posterior communicating artery (red *) is illustratedFigure 2: Postcontrast T1-weighted sequence with maximum intensity projection/multiplanar reconstruction protocol in the axial oblique view with different intensities (a and b). The labels are the same of Figure 1a. On both panels, the two venous channels substituting the telencephalic segment of the right BVR are shown, and their joining occurs at the mid-portion of the diencephalic segment (black >>). Note the drainage of the mesencephalic segment, to the VoG on both sides, including the joining of the internal cerebral veinFigure 3: Postcontrast T1-weighted sequence with multiplanar reconstruction protocol but without maximum intensity projections protocol in the axial oblique view, showing, in both a and b, a similar picture as in Figure 1a and b, i.e., the BVR on (a) and the posterior cerebral artery in (b)Figure 4: Postcontrast T1-weighted sequence with maximum intensity projections/multiplanar reconstruction protocol in sagittal right paramedian view (a) and the corresponding magnified portion corresponding to the basal vein of Rosenthal (b). In both panels, the two venous channels substituting the telencephalic segment are well evident, in an up and bottom position. The up position is kept by the uncal vein–superficial middle cerebral vein (white >), and the bottom position by the deep middle cerebral vein (white *). This last one has an anterior segment ending into the cavernous sinus. ICA: Internal carotid artery, PComA: Posterior communicating artery, CS: Cavernous sinusFigure 5: Postcontrast T1-weighted sequence with maximum intensity projections/multiplanar reconstruction protocol in sagittal right paramedian view (a) and left paramedian view (b). The difference in the telencephalic segment of the basal vein of Rosenthal is evident, with two separated venous channels in (a) and a single continuous vein in (b)Figure 6: Postcontrast T1-weighted sequence with multiplanar reconstruction protocol in the axial view with a magnified detail of the mesencephalon from bottom to up (a-h), showing the ending of the right deep middle cerebral vein (white *) into the cavernous sinus and its course up to the appearance of the uncal vein–superficial middle cerebral vein in a superior position (g) and the joining of the two veinsFigure 7: Postcontrast T1-weighted sequence with maximum intensity projections/multiplanar reconstruction protocol in the axial oblique plane focused on the midbrain (a) and on the course of the uncal vein–superficial middle cerebral vein (UV-SMCV) on the right side (b) and on the course of the left basal vein of Rosenthal with a normal pattern (c). It is well evident the continuity between the UV and the SMCV on the right sideFigure 8: Postcontrast T1-weighted sequence with maximum intensity projections (MIP)/multiplanar reconstruction protocol in the axial view (a and b) and in the sagittal right paramedian view (c and d). (c) A reformatted sagittal view from source images without MIP. Yellow arrow: Cavernous sinus; blue arrow: Sphenoparietal sinus; red arrow: SMCV, white arrow: Anastomosis between the SMCV and the sphenoparietal sinus (a-c). Red arrow: Superficial Sylvian vein; green arrow: vein of Labbè (d)Figure 9: Postcontrast T1-weighted sequence with maximum intensity projections/multiplanar reconstruction protocol in the axial view (a and b) with different obliques (superior in [a] and inferior in [b]). The arrows have the same meaning as in Figure 8a-c. The superficial middle cerebral vein (SMCV) is labeled as white >. The anastomotic channel between the right SMCV and the sphenoparietal sinus is well evident (white arrow), with a medial ending into the cavernous sinus and a lateral ending into the superficial Sylvian veinAmong the intracranial veins, the BVR is notable for its relative stability; however, it is still subject to considerable morphological and functional variability.[1-5] This case describes a unique and previously unreported anomaly in the telencephalic segment of the BVR, with two venous channels joining at the diencephalic segment. The drainage to the CS and the superficial venous system was evident on the right side, contributing to the anomaly through a direct connection between the SMCV and the superficial Sylvian vein, draining into the sphenoparietal sinus and a tributary of the lateral sinus at the same point of the vein of Labbè, lacking an anastomotic pattern on the right hemisphere. Conversely, the lateral mesencephalic vein (LMV) was not prominent, and a drainage pathway to the posterior fossa veins and the superior petrous sinus was not identified.[6-8] In the early phases of embryogenesis, there were three different veins, i.e., the primitive telencephalic, diencephalic, and mesencephalic veins, draining separately into the tentorial sinus.[9] The elongation and narrowing of this tentorial sinus, due to the posterior expansion of the cerebral hemispheres, leads to the development of a unique vein as a direct and short connection. Throughout fetal growth, the BVR evolves into its three main segments, each serving as drainage pathways for their respective regions.[10,11] The telencephalic segment begins where the anterior cerebral vein, DMCV, and inferior striate vein converge, extending from the Sylvian fissure and traversing close to the cerebral peduncle over the uncus. Due to its position, the telencephalic segment connects to the CS via the UV.[11] The diencephalic segment is located in the cisterna ambient and surrounds the cerebral peduncle. The mesencephalic segment starts from the lateral mesencephalic sulcus and reaches the quadrigeminal cistern, draining in the VoG together with the internal cerebral vein (ICV). The LMV connects the ventral diencephalic and mesencephalic veins, and it contributes to the superior petrosal sinus drainage pathway in about 69% of cases.[12] In our case, the DMCV is an isolated medial venous channel connected anteriorly to the CS and, after a backward course, joins the lateral anastomotic channel (UV-SMCV) at a level corresponding to the mid-portion of the diencephalic segment. Thus, a recognizable telencephalic segment is absent. Interestingly, the termination of the UV was investigated in a subset of normal subjects, revealing the UV presence in 118 sides (74%). The UV termination pattern was into the SMCV (48%), the CS (34%), the laterocavernous sinus (13%), and the paracavernous sinus (3%).[12] The complex UV SMCV is not rare among normal subjects. The deep telencephalic vein gives origin to the DMCV and anterior cerebral vein at approximately the 40-mm embryonic stage.[3,9,13] In the same stage, the ventral diencephalic vein drains into the transverse sinus through the primitive tentorial sinus.[3,9,13] This primitive drainage pathway remains briefly after birth. Subsequently, the drainage route for the SMCV and DMCV progresses through the sphenoparietal sinus into the CS. The mesencephalic vein forms the LMV, linking it to the ventral diencephalic vein on one side and the mesencephalic vein on the other side.[8,9,13,14] The deep telencephalic vein gives origin to the UV, which communicates with the basal vein, SMCV, and CS, allowing a wide range of variations in uncal venous drainage patterns.[15] The BVR shows more variation than primary transverse veins, being constituted later in the embryogenesis. Typically, the SMCV does not drain into it, but in this case, it drains into the diencephalic segment of the BVR through an anastomotic UV. In addition, the SMCV contributes to drainage through an indirect path toward both the CS (via the sphenoparietal sinus) and the lateral sinus (through the superficial Sylvian vein). However, in the adult pattern, the telencephalic segment of the BVR drains directly or indirectly into both the BVR and VoG.[16] Suzuki et al.[17] described this variability using 3D CT angiography in a sample of 250 patients and classifying the telencephalic segment as draining (I) into the CS, sphenoparietal sinus, or SMCV; (II) into the second segment; or (III) both routes. The anastomoses between the telencephalic and diencephalic segments and the second segment were not confirmed in 36.9% of cases. In our case, the telencephalic segment was aplastic, substituted by two distinct venous channels – a lateral one corresponding to the UV and SMCV, and a medial one corresponding to a primordial DMCV – resulting from a shift in the joining of the two channels, typically giving rise to the telencephalic segment of the BVR, likely during the embryonic stage when CS annexation occurred. Therefore, only about half of BVRs (55.4%) present this typical configuration, and almost half of BVRs (46.4%) showed anastomoses between the telencephalic segment and the anterior fossa sinuses.[18] The variations of the BVR pathways were classified into four groups:[19] (I) telencephalic group; (II) diencephalic group; (III) tegmental bridging group (LMV anastomosis); and (IV) tectal group. Unfortunately, the pattern described in this case does not easily fit into this classification, and the position of the primitive tentorial sinus is posterior to the anastomotic channel between the SMCV and the sphenoparietal sinus [Figures 8 and 9]. Thus, it is not straightforward to consider this anastomosis a remnant of the anterior end of the primitive tentorial sinus, although this possibility cannot be entirely excluded. More pragmatically, Benet et al.[20] on 4D CTA proposed a classification of BVR into mature and immature types based on the imaging of a connecting channel (diameter > 0.5 mm) with the DMCV and anterior cerebral vein. A fully mature BVR was defined when tributaries from the DMCV and anterior cerebral vein were evident, and the DMCV had a dominant outflow role to the CS. According to this classification, the right BVR in the presented case is defined as “mature,” despite the aplastic telencephalic segment. This classification is straightforward and holds potential operational significance, yet it retains certain embryological considerations. The immature BVR may drain through either the middle sylvian vein (MSV) or the anterior cerebral vein. The MSV serves as a significant connecting vessel, facilitating the superficial drainage of the DMCV into the SMCV.[21] From an embryological perspective, the early tentorial sinus gradually evolves into a sequential fusion of venous tributaries, ultimately forming the mature BVR. Any disruption in these segments results in an immature BVR. Immature BVRs (69%) were prevalent over mature ones (32%). In the presented case, the DMCV drains into the CS, and the SMCV drains both into the CS through the sphenoparietal sinus and into the lateral sinus through the superficial Sylvian vein, displaying an uncommon pattern [Figures 8 and 9]. The Suzuki classification[22] of the superficial Sylvian venous drainage pathways includes: (I) sphenoparietal type (54%); (II) emissary type (12%); (III) cavernous type (7%); (IV) superior petrosal type (2%); (V) basal type (2%); (VI) squamosal type (2%); and (VII) undeveloped type (9%). In this case, the SMCV joined the sphenoparietal sinus with the DMCV on one end and the lateral sinus on the other end alongside the vein of Labbè, lacking the anastomotic configuration on the right lateral hemisphere.[9,23-26] In the present case, the intracranial venous anomaly was an incidental finding, and no causal or therapeutic reasoning was needed. The same anatomical variant may deserve a different attention in a patient with cerebral venous thrombosis or an arteriovenous malformation, but also in case of a highly vascularized tumor, as meningioma, due to the relevance of venous drainage for the surgical planning. In conclusion, this case highlights a rare anomaly in the telencephalic segment of the BVR, characterized by the presence of two distinct venous channels converging at the diencephalic segment. This unique configuration leads to atypical drainage patterns to the CS and superficial venous system, notably lacking the typical anastomotic structure. The findings emphasize the variability in BVR anatomy due to embryological development, demonstrating the importance of recognizing these variations for surgical planning and intervention. In addition, advanced imaging techniques such as SWI and postcontrast T1-weighted MRI are invaluable for visualizing these complex venous networks, enhancing our understanding of their anatomical and functional roles.[27,28] Author contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Marialuisa Zedde and Rosario Pascarella. The first draft of the manuscript was written by Marialuisa Zedde and Rosario Pascarella. All authors read and approved the final manuscript, met the requirements for authorship, and believe that the manuscript represents honest work. Ethical policy and institutional review board statement Not applicable. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed. Data availability statement Data sharing is not applicable to this article as no datasets were generated and/or analyzed during the current study. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.