Third Cranial Nerve Palsy Complicating Peri Mesencephalic Non Aneurysmal Subarachnoid Hemorrhage: A Case Report ()
1. Introduction
Peri mesencephalic subarachnoid hemorrhage (PMSAH) was first described by Van Gijn in 1985 as a rare and distinct subtype of subarachnoid hemorrhage (SAH). It is characterized by the presence of localized bleeding confined to the peri mesencephalic and prepontine cisterns, in the absence of aneurysmal rupture or any other identifiable source of bleeding on cerebral angiography [1]. Patients usually present with a relatively benign clinical course with symptoms often limited to acute or subacute headache, neck pain, and occasionally transient neurological deficit. Cranial nerve involvement is rare and has only been reported in the literature in very few cases. This case highlights an unusual presentation of PMSAH, manifesting as third cranial nerve palsy, and discusses its clinical implications and underlying pathophysiological mechanisms.
2. Case Presentation
We report the case of a 51-year-old man with poorly controlled type 2 diabetes mellitus treated with oral antidiabetic agents. Few hours after sexual intercourse, he developed a sudden onset of thunderclap headache associated with vomiting. One week later, patient noticed upon awakening a vertical binocular diplopia and a partial right-sided ptosis. The patient did not seek medical care until day 8 after symptom onset.
Upon admission to the emergency department, neurological examination revealed a conscious, alert and oriented patient, impaired eye movements except abduction with no direct and indirect light reflexes indicating a complete third cranial nerve palsy. No other neurological deficits were observed neither neck stiffness. General physical examination was normal.
A non-contrast brain CT with angiography (CTA) was performed immediately at admission and showed perimesencephalic subarachnoid hemorrhage, with no evidence of aneurysm or vascular malformation. This initial imaging enabled the exclusion of aneurysmal SAH at presentation. Brain MRI demonstrated hyperintense signals on FLAIR, diffusion, and T2-weighted images (Figures 1-4), consistent with subarachnoid blood in the prepontine and peri mesencephalic cisterns, suggestive of a PMSAH. Cerebral digital subtraction angiography was scheduled on day 12 post symptom onset as a confirmatory, rather than diagnostic, step. The DSA remained negative for aneurysm or vasospasm (Figure 5).
Figure 1. Brain MRI, FLAIR sequence. (a) Axial view and (b) sagittal view showing hyperintensity in the perimesencephalic region, consistent with PAMSH (red arrow).
Figure 2. Brain MRI, T2-weighted sequence. (a) Coronal view (2.3 mm thickness) showing subtle hyperintensity in the midline perimesencephalic region. (b) Axial view (4 mm thickness) where no evidence of perimesencephalic hemorrhage is visible.
Figure 3. Brain MRI, diffusion-weighted sequence (slice thickness: 5 mm): hyperintense signal in the midline perimesencephalic region consistent with a perimesencephalic subarachnoid hemorrhage (red arrow).
Figure 4. Brain MRI, orbital T2-weighted fat-suppressed sequence (slice thickness: 2.2 mm): hyperintense signal in the midline perimesencephalic region consistent with PMSH (white arrow).
Figure 5. Cerebral angiography of the posterior circulation showing no abnormalities.
Lumbar puncture revealed xanthochromic cerebrospinal fluid containing 25 white blood cells, 6 red blood cells, a protein level of 0.42 g/l, and glucose level of 1.5 g/l. Blood tests including electrolyte panel, liver and renal function tests, complete blood count, C-reactive protein, thyroid function, hepatitis and HIV serologies were all within normal limits, except for hyperglycemia (3.13 g/L) and elevated HbA1c (9.5%) without ketosis. Notably, the patient exhibited no evidence of diabetic microvascular complications, such as retinopathy or neuropathy, upon ophthalmologic and neurological examination.
A final diagnosis of PMSAH was made, likely triggered by sexual activity in the context of poorly controlled diabetes. The third nerve palsy was considered a delayed complication. Patient was treated with analgesics only and optimization of glycemic control. A spontaneous and complete recovery of both the third cranial nerve palsy and headaches was observed three months later. Unfortunately, the patient was transferred to another city for follow-up care and was only contacted by phone to confirm the clinical resolution of symptoms. No imaging studies were performed to document the resolution of the hemorrhage.
3. Discussion
PMSAH is a rare condition with a low incidence estimated at 0.3 - 0.5 cases per 100,000 inhabitants. It accounts for only 5% to 10% of all SAH and less than 30% of non-aneurysmal SAH [2]. PMSAH differs from other types of SAH by an earlier age of onset, typically around 50 years [3], a lower prevalence of hypertension, and a strong association with physical efforts and the Valsalva maneuver. This last point is a notable feature of PMSAH. Indeed, our patient’s headaches occurred following sexual activity. Similarly, in Foreman et al.’s series, 16 patients developed PMSAH after coitus or masturbation [4]. A hyperdynamic circulatory state during sexual activity may trigger SAH, possibly through transient hypertensive peaks.
The exact pathophysiological mechanism underlying PMSAH remains unclear. Given the normal angiographic findings, limited hemorrhage extension, and benign clinical signs, a venous origin has been suggested in several reports [5]-[7]. Investigations into venous drainage in PMSAH patients propose rupture of the basal vein of Rosenthal (BVR) or its tributaries, including the interpeduncular veins or posterior communicating veins, as possible causes [5]. The rupture of the BVR is the most common theory; a primitive anatomical variant (type C) can divert blood drainage away from the vein of Galen which makes the BVR more fragile and prone to rupture (Figure 6).
Clinically, PMSAH usually presents with acute-onset headaches evolving over a few hours. Focal neurological deficits, transient consciousness disturbances and seizures are rare, reflecting the generally benign course of this hemorrhage. According to Sahin et al. [8], only 7% of patients were classified as grade III or higher on the Hunt and Hess scale for SAH, while 93% were grade I or II. A Moroccan study including 24 patients with PMSAH between September 1999 and June 2009 reported that 80% were admitted with grade I, and only two patients had grade IV on the Hunt and Hess scale [9].
Our patient developed binocular diplopia due to third cranial nerve palsy complicating PMSAH in the context of physical effort (sexual activity) and poorly controlled diabetes. Diabetic microvascular third nerve palsy is well-known; diabetes likely acted as a cofactor along with the post-coital trigger in the development of the cranial nerve III palsy. This complication is exceptional in PMSAH and has rarely been reported. Roman et al. [2] described a series of seven patients, five of whom had diplopia or ocular motor palsy associated with headaches. Abbatemarco et al. [10] reported a 63-year-old woman presenting with severe headaches and total third nerve palsy related to non-aneurysmal PMSAH. Two other cases of painful third nerve involvement in PMSAH were described by Kamat et al. [11] and Sakashita et al. [5]. The exact pathophysiological mechanism remains uncertain but hypotheses include: direct nerve compression by hematoma mass effect, ischemic injury due to occult vasospasm undetectable by angiography, or a small mesencephalic ischemic stroke secondary to vasospasm [10] [11]. In our patient, the seven-day delay between headaches onset and cranial nerve palsy suggests a mechanism involving vasospasm-induced ischemia of the nerve, possibly exacerbated by diabetes-related vulnerability.
Brain MRI combined with arterial angiography is the key diagnostic tool for PMSAH, enabling detection of subtle hemorrhages missed by CT and identification of aneurysms. Vessel wall MRI may also aid diagnosis by directly visualizing vessel wall changes [2]. However, cerebral angiography remains the gold standard for definitively excluding aneurysms. In our case, diagnosis was established by MRI and angiography ruling out aneurysmal cause.
Although PMSAH is generally benign, it is not without complications. Wolfert et al. [12] reported a series of 71 patients, of whom 35% developed complications including hydrocephalus, delayed arterial vasospasm, and cerebral ischemia, increasing mortality risk by 3%. Regarding prognosis, our patient achieved complete recovery within three months with a Rankin score of 1. This aligns with the Moroccan study showing favorable long-term outcomes after a mean follow-up of 38 months: 50% of subjects became completely asymptomatic, and 45% had only mild headaches with no seizures or rebleeding observed [8].
Figure 6. Venous angiography the different variants of the basal vein of Rosenthal according to Watanabe’s classification: Type A: continuous normal vein; Type B: discontinuous normal vein; Type C: primitive variant.
4. Conclusions
This case highlights a rare and intriguing presentation of PMSAH initially manifesting as an isolated third cranial nerve palsy in the setting of post-coital exertion and poorly controlled diabetes mellitus. While PMSAH is generally considered a benign subtype of subarachnoid hemorrhage with a favorable prognosis, this case demonstrates the importance of recognizing that cranial nerve involvement particularly of the oculomotor nerve may occur even in the absence of an aneurysm or mass effect. The delayed onset of third nerve palsy, in this context, may point toward transient ischemic mechanisms such as occult vasospasm, especially when compounded by vascular risk factors like diabetes. Clinicians should be aware of this rare but possible complication, as early recognition may facilitate more tailored investigations and appropriate follow-up. Further studies are warranted to elucidate the exact pathophysiological processes involved and to better define the prognostic implications of cranial nerve involvement in PMSAH.
Emergency physicians and neurologists should include perimesencephalic subarachnoid hemorrhage in the differential diagnosis of acute, isolated cranial nerve III palsy especially following a thunderclap headache and even when aneurysm is not immediately apparent. Early high-resolution CTA and/or MRI is recommended, and in individuals with vascular risk factors, a sustained level of vigilance is essential.
Authors’ Contributions
Bayoum Zineb, Mounia Rahmani: writing the manuscript and collecting clinical data.
Meriem Fikri: Collecting the radiological data.
Najoua Maarad: Collecting clinical data.
Wadie Bnouhanna, Maria benabdejlil, Aidi Saadia: Reviewed the manuscript.
Funding
This research received no external funding.
Informed Consent Statement
Informed consent was obtained from the patient for publication of this case report and accompanying images.
Conflicts of Interest
The authors declare no conflicts of interest.