Introduction

The incidence of spinal cord infarction is estimated to be 3.1 per 100,000 person-years or about 7600 cases per year in the United States [1]. Symptom onset is typically rapid and severe, and can include burning back pain, weakness and paralysis, loss of pain and temperature sensation, loss of deep-tendon reflexes, autonomic dysfunction, and neurogenic bowel/bladder. Although often of iatrogenic cause (e.g., intra-operatively during aneurysm repairs), spinal cord infarctions can also be caused by hypotension, atherosclerosis, atherothrombotic as well as fibrocartilaginous emboli, hypercoagulability, AV malformations, vasculitis, dissection, and trauma [2]. Zalewski et al. reviewed 133 patients with spontaneous spinal cord infarctions, finding the mean age to be 60 years and the causes to be idiopathic with atherosclerotic risk factors in 68% of cases, due to fibrocartilaginous embolism in 14%, aortic dissection in 5%, hypercoagulability in 4%; vertebral artery dissection in 3%; systemic hypotension in 2%; cardioembolic in 2%, and vasculitis in 2%.

The anterior spinal artery (ASA) is the most frequently implicated in spinal cord infarction, although several variable patterns of infarctions exist. In a retrospective review of 27 spinal cord infarction patients by Novy et al., 37% of the patients presented with bilateral anterior spinal cord infarctions, 15% anterior unilateral infarcts, 15% posterior unilateral, 11% central, 7% posterior bilateral, and 7% transverse [3]. The ASA, which supplies the anterior two-thirds of the spinal cord, is rostrally normally formed by the convergence of one descending branch from the fourth segment of each of the vertebral arteries [4, 5]. Often, one of the branches tend to be dominant, whereas the other can be hypoplastic; the left vertebral artery (LVA) is dominant in 50–60% of cases [6, 7]. As the ASA progresses in the caudal direction within the cervical spine, it may receive additional contributions from the thyrocervical trunk, costocervical trunk, inferior thyroid arteries. deep cervical arteries (e.g., artery of cervical enlargement), and ascending cervical arteries, as well as further contributions from the vertebral arteries [4, 5]. It is understood, however, that there is considerable individual variation in this arterial network [4].

In this case report, we present a patient with “Man-in-the-Barrel” syndrome due to extrinsic osteophytic compression (at the upper thoracic level) of an anomalous non-dominant right vertebral artery (RVA) arising aberrantly from the descending aorta and inserting aberrantly into the left posterior inferior cerebellar artery, leading to hypoperfusion and C2–C5 cord infarction.

Case presentation

We present a 48 year old male with history of hypercholesterolemia, peripheral neuropathy, sleep apnea, and generalized anxiety disorder who experienced sudden onset neck pain when jumping on a chair at his workplace during which he reportedly twisted his neck. Symptom onset was not preceded by a large meal or oral bolus. Pain was described as a shooting sensation down his spine. This was followed by weakness in his upper and lower extremities, to the point where he could barely walk. Patient had reportedly taken benzodiazepine and opioid medications after the event. On arrival to the hospital, he appeared to be obtunded and lethargic with minimal verbal response and pinpoint pupils, and concern for acute hypoxemic respiratory failure (SpO2 79%) secondary to drug-related toxic metabolic encephalopathy. Based on laboratory studies revealing opioid and benzodiazepine intoxication, he was treated with fluids and naloxone. His mental status improved with medical management. Imaging of the brain was unremarkable. CT of the cervical spine showed non-specific cervical spondylosis without acute fracture or subluxation. CT angiogram of the neck was negative for vascular occlusion, dissection, or aneurysm. MRI of the cervical spine demonstrated T2 signal abnormality involving the anterior aspect of the spinal cord from C2 to C5 consistent with spinal cord ischemic insult within the distribution of the ASA (Fig. 1). MR angiography of the neck confirmed no dissection or stenosis involving the bilateral common or internal carotid arteries but did show a small, irregular RVA that terminated in the posterior inferior cerebellar artery (PICA) (Fig. 2). He was started on aspirin and discharged to an acute inpatient rehabilitation facility at a maximal assist level for transfers, moderate assist level for gait, and minimum to total assistance for ADLs.

Fig. 1
figure 1

T2-weighted MRI of the cervical spine revealing increased signal intensity of the anterior cervical spinal cord at C2 to C5 (three arrows) seen on sagittal view (A) and “owl-eyes” sign (two arrows) on axial view (B), suggesting anterior territory ischemia.

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Fig. 2
figure 2

Axial CT angiogram showing hypoplasia of the right VA (small arrow) relative to the left VA (large arrow) (A). The dominant left VA terminates into the basilar artery (star) and the hypoplastic right VA terminates into the right PICA (arrowhead) (B, C).

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Upon initial evaluation at the rehabilitation center, he presented in no acute distress with normal vital signs. Neurological exam was conducted in reference with the ASIA/ISCoS International Standards for Neurological Classification of Spinal Cord Injury, and revealed 3/5 strength in the right elbow flexors, 1/5 strength in the left elbow flexors, 4/5 strength in the right wrist extensors, and 4/5 strength in the left wrist extensors with mild spasticity throughout the bilateral upper extremities. Remainder of major muscle groups including the lower extremities demonstrated 5/5 strength bilaterally. Sensation to pinprick and light touch were impaired in all levels below C3. Cardiac, pulmonary, and abdominal examinations was unremarkable. He exhibited neurogenic bowel and bladder. His gait was ataxic. After an inpatient rehabilitation program for 2 weeks, the patient was discharged home at a minimum assistance to modified independent level with outpatient physical and occupational therapy.

He continued to have significant neurological deficits in the upper cervical distribution when seen as an outpatient 1 month later. Further review of the initial CT angiogram revealed a contact between the RVA and an anterior T2–T3 osteophyte (Fig. 3). A spinal angiogram was then performed which revealed a dominant LVA (Fig. 4). In addition, it also demonstrated the RVA originating directly from the descending thoracic aorta, crossing midline in the thoracic region, and terminating into the right-sided posterior circulation (Fig. 5). Additional blood supply to the ASA was noted on the angiogram to be from the left thyrocervical trunk at the level of C6 to C7 and the right segmental artery at the level of T4.

Fig. 3
figure 3

Axial CT angiogram revealing the right VA (arrow) branching off the descending thoracic aorta (A) and contacting an anterior thoracic osteophyte upon crossing midline posterior to the esophagus at T2–T3 (B).

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Fig. 4
figure 4

Spinal angiography of the posterior circulation showing dominance of the left VA (large arrow), which terminates into the basilar artery (star).

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Fig. 5
figure 5

Spinal angiography demonstrating the origin of the right VA from the descending aortic arch (A) and crossing midline in the upper thoracic region (B).

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The patient was seen by neurosurgery and no surgical intervention was recommended. He continued with physical and occupational therapy. Four months after the initial infarction, he had negligible improvement in his upper extremity weakness. Patient was able to ambulate independently but required assistance for bathing and dressing. His spasticity, neurogenic bladder, and neurogenic bowel remained well controlled with medications and behavioral modifications.

Discussion

This case reports a rare case of “Man-in-the-Barrel” syndrome secondary to cervical cord hypoperfusion. Man-in-the-Barrel syndrome is a known phenomenon of brachial diplegia involving proximal paresis of the upper extremities with preservation of strength in the lower extremities [8]. While typically seen in the setting of cerebral hypoperfusion at the border zones between the anterior and middle cerebral artery territories, it has also been reported to rarely occur following ASA-territory cervical spinal cord infarction stemming from vertebral artery thrombosis or dissection [9,10,11,12]. This is the first known case of cervical cord infarction and Man-in-the-Barrel syndrome to occur in the setting of an aberrant RVA being compressed by an anterior thoracic osteophyte.

The cervical spinal cord is supplied by one anterior and two posterior spinal arteries. The vertebral arteries, which normally arise from posterosuperior aspect of the respective ipsilateral subclavian arteries, travel though the transverse foramen in the cervical spine and contribute directly to the anterior and posterior spinal arteries. These two branches are often not equal in contribution, and dominancy of one vertebral artery is common [4, 6]. In historical cases, ASA syndrome secondary to vascular infarction has been demonstrated to occur via vertebral artery dissection or severe stenosis [13, 14]. This case demonstrates a unique instance in which a patient sustained a spinal cord infarction in the setting of anomalous RVA noted to be compressed by an anterior thoracic osteophyte, likely leading to decreased flow through the ASA and Man-in-the-Barrel syndrome.

In our patient, while the dominancy of the LVA was not surprising, the origin of the RVA from the descending thoracic aorta is striking. Yuan et. al. reviewed 1286 patients with aberrant vertebral arteries and found that some aberrant arteries had a single site of origin while others had dual origin [15]. Among patients with aberrant vertebral arteries of single origin, the LVA was implicated most frequently (85.6%), the RVA (11.7%) less commonly, and bilateral vertebral arteries (2.7%) least commonly, with only one patient in this entire compilation exhibiting an aberrant RVA arising directly from the descending aorta (as seen in this case) [15]. However, aberrant origin of the vertebral arteries is not usually symptomatic, and in most cases do not result in neurologic sequalae. In the same review, only 5.5% of patients with aberrant vertebral arteries exhibited syndromes attributable to the arterial variations [15].

Another less striking but likely clinically significant anatomical variation in this patient was the insertion of the RVA into the left PICA. Normally, the LVA and RVA converge at their rostral end to form the basilar artery. A branch from each of the vertebral arteries slightly caudal to this convergence give rise to the respective PICAs bilaterally. The insertion of vertebral arteries into the PICA is a well-known anatomic variant [16]. It is frequently associated with decreased caliber of the PICA-inserting vertebral artery, and even vertebral artery hypoplasia [6, 17]. In one review of patients with ischemic strokes in the vertebrobasilar artery distribution, it was found that vertebral artery insertion into the PICA was seen in ~8% of patients [18]. Furthermore, multiple case reports have documented that in patients with a hypoplastic vertebral artery that inserted into the PICA, there was an increased risk of rotational vertebral artery occlusion associated with ipsilateral head rotation, although the infarctions in these cases were primarily in the inferior cerebellum and lateral medulla [19,20,21]. Despite these associations, the clinical significance of aberrant insertion of the vertebral artery into the PICA remains unclear and disputed [6]. In the general population, it has been estimated that ~2% of otherwise healthy individuals have RVA insertion into the right PICA [16]. In our patient, however, the combination of aberrancies in both the origin and termination of the RVA may have additively contributed to the C2–C5 watershed region. In addition, this was likely additionally exacerbated by the lack of other major arterial contributions in the region. Classically, there exists a large branch from the vertebral arteries supplying the ASA around the level of C3 [4]. However, in our patient, there was no such contribution from either side, and the next significant branch was from the left thyrocervical trunk at C6-7.

Another significant contributor to the patient’s clinical presentation was the presence of anterior vertebral osteophytes at the T2–T3 level. Anterior vertebral osteophytes have been very infrequently reported in the literature. Case reports exist of anterior cervical osteophytes causing dysphagia and sleep apnea, and anterior lumbar osteophytes affecting the inferior vena cava and abdominal aorta [22]. Anterior thoracic osteophytes are most commonly observed on the vertebral bodies of T9 and T10 [23]. Per several sporadic case reports, anterior thoracic osteophytes have been associated with dysphagia in the supine position, compression of the sympathetic trunk and splanchnic nerves, trauma to the descending aorta, pseudoaneurysm formation, obstructive pneumonia, and right-sided lung fibrosis [24,25,26,27,28,29,30]. However, none of the above cases involved thoracic osteophytes as high as T2–T3 or have been associated with spinal cord infarction.

In summary, this case illustrates a rare scenario in which multiple structural/developmental anomalies predisposed towards a watershed region at C2–C5, which then was acutely infarcted upon acute rotation of the neck. It is likely that compression of the RVA led to ischemia of the central anterior horn cells in a region that lacked other major collateral contribution. This resulted in the Man-in-the-Barrel syndrome, in which the central anterior horn cells are focally affected. The lack of improvement in his symptoms correlated with the expected outcomes following spinal cord infarction. True anterior cord syndrome and posterior cerebral infarction were likely averted due to dominant circulation from LVA, as well as collateral circulation from the thyrocervical trunk and segmental arteries. Dominancy of the LVA may also have provided adequate vascular coverage throughout the patient’s life until the acute triggering events described.

To our knowledge, this is the first documented case involving osteophytic vertebral artery compression resulting in spinal cord infarction. Further research on the developmental and pathophysiologic processes underlying these anomalous anatomic variations is needed. Future initiatives to improve patient screening and early detection may be valuable to improve risk stratification and aid in primary prevention for patients predisposed to spinal cord infarction.