Cavernous region dural fistulas with venous drainage of laterocavernous sinus
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.79135
Source of Support: None, Conflict of Interest: None
Background : We present our findings concerning the laterocavernous sinus (LCS) drainage of cavernous region dural fistulas, focusing our attention on the anatomy of LCS as it may have important implications in the treatment. Patients and Methods : Thirty-one consecutive patients with cavernous region dural fistulas treated endovascularly between 2005 and 2008 were reviewed. Five patients had angiographic features such as cavernous region dural fistulas draining with superficial middle cerebral vein (SMCV) via LCS. Clinical records of these 5 patients were focused upon to determine their presenting symptoms, angiographic features, endovascular treatments and clinical outcomes.
Keywords: Arteriovenous fistula, dural, laterocavernous sinus
The laterocavernous sinus (LCS) is a venous structure located in between the two dural layers forming the lateral wall of the cavernous sinus (CS), and LCS has been described as one of the principal drainage pathways of the superficial middle cerebral vein (SMCV). Venous structures of the laterocavernous sinus may also be involved in a cavernous region dural fistula, either independently or in conjunction with CS, which may represent a diagnostic pitfall with important implications for the planning and success of the endovascular procedure. ,, LCS as an accessible compartment has been selectively used for embolization of cavernous dural arteriovenous fistulas (DAVFs). ,,, LCS, although small, includes several important deep-tissue extracranial and intracranial structures involved in a variety of disease processes.  LCS has importance in multiple clinical situations, in which interventional neuroradiological management plays a central role.  In this article, we present our findings concerning the cavernous region dural fistulas involving LCS drainage, focusing our attention on the anatomy of LCS as it may have important clinical implications.
From 2005 to 2008, 31 patients with cavernous region dural fistulas were treated with endovascular techniques at our institution. Pre-therapeutic angiography included bilateral selective injection of the external and internal carotid arteries and vertebral arteries. When performing angiography for the assessment of cavernous region dural fistulas, care was taken on the venous phase of both external and internal carotid arteries to demonstrate a cortical drainage. Among these patients, SMCV drainage via LCS was noted in 5 (16%) patients. Hospital records, angiograms and procedure reports were retrospectively reviewed. The characteristics, methods of treatment, and approach with regard to the 5 patients are summarized in [Table 1]. There were 2 men and 3 women, with age in the range of 22-49 years.
All 5 cavernous region dural fistulas were cured by endovascular techniques. Procedures were performed preferably with general anesthesia. The endovascular treatment included transarterial embolization in 3 and transvenous embolization in 2 patients. Clinical follow-up ranged from 9 to 26 months (mean, 18 months). Cure was defined as complete resolution of the presenting symptoms during the observation period.
Five (16%) patients out of 31 were retrospectively reviewed [Table 1]. In these 5 cases, leptomeningeal veins (SMCV, PV) reflux via LCS caused by cavernous region fistula was noted. The LCS is identified on the anteroposterior projection as a slit-like structure draining SMCV [Figure 1]. This inner layer may be seen as a thin vertical opacification defect between LCS and the lateral compartment of CS when these venous spaces are visible together.
Initial presenting symptoms included proptosis (n=1), chemosis (n=2), ophthalmoplegia (n=1), intracranial bruits (n=3) and headaches (n=1).
Three fistulas were located on the left cavernous sinus; 2 were on the right. According to the Cognard classification, the venous drainage in all cases was type III and Barrow type A (1/5), B (1/5), C (1/5) and D (2/5).
All 5 patients underwent immediate obliteration of the cavernous region dural fistulas in 3 sessions of transarterial and 2 sessions of transvenous embolization. Arterial embolizations were performed with coils (n=1), Onyx 18 (M. T. I.-ev3, Irvine, CA) (n=1) [Figure 1] and detachable balloon (1#, Balt, Montmorency, France) (n=1). Transvenous embolization was accomplished by packing the affected sinus segment with fibered platinum coils (n=1) and Onyx+coils (n=1) [Figure 2].
Clinical follow-up in mean 14.8 months
Cure was defined as complete resolution of the presenting symptoms during the observation period (mean, 18 months). We encountered one minor complication of local hair loss induced by X-ray radiation. A complete resolution of the initial presenting symptoms was observed within a few days to weeks. Angiographic follow-up Six-month follow-up angiogram in 5 patients showed obliteration and no recanalization of the fistulae.
The findings reported here are consistent with the concept that the laterosellar blood spaces could be divided into two embryologically, morphologically and functionally independent systems with potential secondary connections:  a medial system made up of the superior ophthalmic vein, CS and the inferior petrosal sinus; and a lateral system draining the cortical blood of the cerebral convexity through SMCV toward the pterygoid plexus and/ or the transverse sinus. The latter pathway may take the form of a paracavernous sinus, an LCS or a classic termination of the SMCV into the anterosuperior aspect of CS, in decreasing order of frequency [Figure 3]. Despite the close topographic relationship between LCS and CS, LCS is sometimes difficult to identify on digital subtraction angiography (DSA) studies; the two structures are separate anatomic entities with distinct functional and clinical implications.  LCS is one of the principal drainage pathways of the superficial middle cerebral vein (SMCV). ,
In a previous study, laterocavernous sinus was found enclosed in the lateral wall of CS in 24.1% of the cases.  In the present study, laterocavernous sinus was found in 16.1% of the cases with CCFs. LCS drains itself principally into SPS or PP as well as communicates with CS in two situations either through a large opening in the posterior aspect of the lateral wall of CS or through small en passant connections located in the medial layer of the lateral wall of CS. If there is no communication existing between the two structures, in the majority of cases, LCS can be considered as an independent venous pathway running parallel to CS, representing one of the main variants in the drainage pattern of SMCV. Four basic drainage pathways have been described for LCS:  1) towards the ipsilateral transverse sinus via SPS; 2) towards the pterygoid plexus via openings in the floor of the middle cranial fossa; 3) towards the posterior aspect of CS; and 4) towards the basal vein of Rosenthal via uncal vein.
The angiographic anatomy of LCS
Angiographically, LCS is readily identified on the anteroposterior projection as a slit-like structure draining SMCV towards any of the above-mentioned terminations.  LCS is the outermost venous structure of the laterosellar region, separated from the lateral compartment of CS by the inner dural layer of the lateral wall of CS. This inner layer may be seen as a thin vertical opacification defect between LCS and the lateral compartment of CS when these venous spaces are visible together. Two anatomic situations must be considered to understand these different patterns of opacification: 1) simultaneous opacification occurs when LCS and CS communicate via large anastomotic channels or when LCS terminates into the posterior aspect of CS; 2) LCS and CS are completely separated or communicate with small en passant connections. 
The primitive tentorial sinus, which drains cortical blood coming from SMCV, migrates medially towards CS region at the time of formation of the lateral wall of CS, during the eighth week of gestation.  Depending on the extent of migration and subsequent formation of anastomoses between the tentorial sinus and CS, three adult SMCV drainage patterns may result: , 1) it terminates into the anterosuperior aspect of CS, seen in 19.5% of patients in a previous study; 2) it courses as an LCS enclosed within the lateral wall of CS, seen in 34% of their patients; or 3) it follows a more lateral trajectory within the dural floor of the middle cranial fossa, where it takes the name of paracavernous sinus, seen in 46.5% of their patients.
Finally it should be noted that LCS may have important clinical implications when involved in the venous drainage of vascular lesions. For example, a dural arteriovenous fistula located on a LCS sometimes cannot be accessed for embolization therapy through a usual endovascular approach, i.e., through the ophthalmic vein or inferior petrosal sinus. ,,,,,, In such cases, knowledge of the existence of an LCS will allow considering alternative therapeutic strategies and avoiding predictable failure of the endovascular procedure. ,,,,, A secondary connection with the basal vein of Rosenthal may also occur through an uncal vein, offering potential collateral flow into infratentorial veins by way of the peduncular and lateral mesencephalic veins. , If present, these connections offer the anatomical substratum for retrograde filling into the superficial and deep venous system in patients with CCFs, placing the patient at a higher risk of hemorrhagic and ischemic complications. 
In our patients with CCFs, LCS was involved. Endovascular access to an LCS may theoretically be obtained by retrograde catheterization of the superior petrosal sinus, PP or the posterior portion of CS, depending on the termination of LCS. In the literature, we found one report of a DAVF involving LCS. San Millαn Ruνz et al. described a case of a DAVF located on an LCS, and it was cured by obliteration of LCS via PP.  In our series, 2 patients were treated transvenously via IPS; an approach to LCS through CS was feasible in one patient, and small en passant connections between LCS and CS were occluded in another patient. The other 3 patients were treated transarterially.
DAVFs involving LCS need to be recognized as a separate entity from CS DAVFs. Failure to angiographically recognize a DAVF of the LCS may lead to the erroneous diagnosis of a CS DAVF. Such a procedure will not only have no effect on the arteriovenous shunt on LCS but may in patients in whom CS represents the major outflow of LCS increase retrograde filling of the cerebral veins draining into LCS, placing the patient at a higher risk of hemorrhagic and ischemic complications. Better knowledge of its course and connection patterns should enable more frequent recognition of LCS on angiographic studies and improved evaluation of its potential clinical implications.
[Figure 1], [Figure 2], [Figure 3]