Filar arteriovenous fistula associated with anomalous common posterior intercostal arterial trunk – A case report and review of literature

Abstract

An anomalous common trunk giving rise to bilateral intercostal arteries at multiple levels is exceedingly rare and its association with spinal filar AVF and low-lying cord has not been reported so far. Here, we report this uncommon anatomical variation in a 60-year-old male who presented with paraplegia and on imaging found to have low-lying spinal cord with filar AVF and venous congestive myelopathy and discuss its embryological basis and associated malformations. Although rare, interventional radiologists should be aware of this entity, as these trunks may be a major source of bleeding in patients with hemoptysis, and also may be involved in vital spinal cord supply.

Introduction

Innumerable variations in the origin, number, area of supply and branching pattern of intercostal arteries have been documented in the literature.^1–4 In majority of cases, there are 11 pairs of intercostal arteries and a pair of subcostal arteries. One of the frequent variations is a common trunk supplying two or more posterior intercostal arterial territory on the same side. This branching pattern is often noted in upper thoracic level at third intercostal space (20–50%), followed by 10th and 11th intercostal level (10–15% per artery).^5,6 An anomalous common trunk giving rise to bilateral intercostal artery at multiple level is exceedingly rare.⁷ To the best of our knowledge, only four cases are reported in literature.^7–10 Here, we report a case of spinal vascular malformation, where in a common posterior intercostal arterial trunk with multiple anomalies were detected on imaging.

Case report

A 60-year-old male presented with gradually progressive weakness in the bilateral lower limbs for 10 months. During the course of illness, he developed difficulty in micturition and constipation. He also had tingling and numbness in both lower limbs. On examination, he was able to stand with support, power in both lower limbs was 4/5, tone was normal, and there were no sensory deficits. His magnetic resonance imaging (MRI) of spine showed low-lying cord reaching up to L3 level with thick fatty filum (Figure 1(a) and (c)). T2 weighted images showed intramedullary T2 hyperintensity in spinal cord at lower dorsal level extending from D5 to L3 level (Figure 1(b)). In addition, tortuous vascular flow voids were noted along the surface of cord in T2 weighted images extending caudally around filum (Figure 1(a) and (b)). Imaging diagnosis of venous congestive myelopathy secondary to spinal vascular malformation was made and subsequently patient underwent spinal digital subtraction angiography (DSA).

Figure 1.

Midline sagittal T2 weighted MR image of whole spine (a) low-lying cord with conus ending at upper border of L3 vertebra (Thick arrows). Midline sagittal T2 weighted MR image of dorso lumbar spine, (b) long segment T2 hyperintensity of cord extending from D5 to L3 level (arrow head). Also note multiple tortuous vascular flow voids along the surface of cord and conus (curved arrow). Axial T1 weighted MR image at the level of S3 showing thick fatty filum (arrow head).

Spinal angiography showed ACPIAT arising from descending thoracic aorta at the level of upper border L1 vertebral from its posterior wall. This artery was seen running superiorly posterior to aorta and was giving rise to bilateral posterior intercostal arteries of D4 to D12 levels (Figure 2(a)). RMA supplying the ASA was arising from left D9 posterior intercostal artery (Figure 2(b)) and seen feeding filar AVF at S1-S2 level with venous drainage retrogradely through filar vein into medullary veins (Figure 2(c) and (d)). Secondary dural feeders are also seen bilaterally at S2 neural foramina supplied by a branch each from bilateral lateral sacral arteries (Figure 2(e) and (f)), and there was no supply from the median sacral artery. Lumbar arteries were identified from L1 to L3 level. At each level, a common trunk was seen dividing into right and left lumbar arteries.

Figure 2.

Frontal early (a) and delayed (b) arterial phase digital subtraction angiographic (DSA) image showing anomalous common posterior intercostal arterial trunk arising from aorta at L1 level (long thin arrow) and supplying bilateral posterior intercostal arteries, also note radiculo-medullary artery arising from left 9th posterior intercostal artery (thin arrow). Selective left 9th posterior intercostal artery DSA arterial (c) and venous phase (d) showing hypertrophied filar artery (arrow head) supplying fistula with early opacification and retrograde filling of filar vein which is overlapping the filar artery (curved arrow). Selective DSA of right (e) and left (f) internal iliac artery showing secondary dural feeders from lateral sacral artery with early opacification of filar vein (Asterix). DSA (frontal view) of inferior mesenteric artery showing abnormal dilated vessels around inferior rectum. (g). (h) DSA (frontal view) showing left gastric artery direct origin from aorta (thick arrow head).

In addition, left internal iliac angiography showed abnormal vascular blush in inferior rectal region with feeders from inferior rectal artery. To characterise this and look for other co-existing abnormalities, we performed complete abdominal angiography. IMA angiogram showed dilated tortuous vessels in the rectum fed by bilateral superior and middle rectal arteries causing early opacification of dilated veins draining into inferior mesenteric vein (Figure 2(g)). Minor arterial contribution was also noted from the bilateral inferior rectal arteries. Left gastric artery was separately arising from the aorta (Figure 2(h)). Bilateral renal, SMA and celiac angiograms were normal.

To look for associated anomalies, we performed CECT of chest and abdomen which confirmed the vascular findings seen on DSA (Figure 3(a) and (b)). ACPIAT was seen in pre-vertebral location at the normal expected location of abdominal aorta, whereas aortic segment supplying gut is seen ventrally placed and seen entering abdominal cavity through oesophageal hiatus (Figure 3(d)) CECT thorax revealed common trunk of left pulmonary vein draining into left atrium (not shown). Bilateral adrenal glands were fused in midline forming horse shoe adrenals (Figure 3(c)). In addition, there were 11 pair of ribs and sacral spina bifida and retro-aortic left renal vein (Figure 3(e) and (f)). After multidisciplinary discussion involving neuroradiologist and neurosurgeon, the patient underwent elective surgery for filar fistula and low-lying cord.

Figure 3.

(a) Volume-rendered CT angiographic image in maximum intensity projection showing ACPIAT (long thin arrow) and rectal angiodysplasia (short thin arrow). (b) Sagittal Multiplanar reconstructed CT angiography image shows relationship between ACPIAT (arrow head) and ventrally placed aorta (dot). Axial contrast enhanced CT image at the level of supra-renals (c), Renal hilum (d), at D10 (e) and S2 level (f) showing midline fused horse shoe-shaped adrenals (short thick arrow), retro aortic renal vein (long thick arrow), ventrally placed aorta exiting through esophageal hiatus (curved arrow to right) and ACPIAT through expected normal location of aorta (curved arrow to left) and posterior spina bifida (thick arrow head).

Discussion

In humans, there are 11 pairs of posterior intercostal arteries. The first two intercostals originate from supreme intercostal artery arising from costo-cervical trunk which in turn is a branch of subclavian artery. Lower nine pairs are the branches of descending thoracic aorta. Innumerable variations in the origin, number and branching pattern of intercostal arteries have been described in literature.^1–5 Variations include hypoplasia, atresia of individual intercostal artery with reconstitution of its supply through anastomotic channels of adjacent segmental arteries. Ipsilateral posterior intercostals supplying single or multiple segments arising from a common trunk are also a frequent anatomical variation, whereas the presence of anomalous common trunk that gives rise to bilateral aortic intercostals is very rare. To best of our knowledge, only four cases are reported in literature (Table 1).

Table 1.

ACPIAT in the literature-Imaging findings and associated anomalies in the reported cases.

Caseno.	Year	Author	Modality	Indication	Findings	Associated anomalies
1	2001	Brew et al.7	DSA	Pre-operative localization of RMA prior to Kyphosis surgery	Common trunk at L1	Kyphosis Ventral displacement of Aorta
2	2009	Chang et al.8	MRA/CTA	Reno vascular hypertension	Common trunk at D12 and D6 level	Isolated splenic artery Replaced right hepatic artery Ventral displacement of aorta
3	2013	Edwards et al.9	CTA	Not Mentioned	Common trunk at D12, RMA from left 7th inter costal artery	Vaginal agenesis Right renal ectopia with common iliac origin of right renal artery Spinal bifida at L5, S1–S3
4	2016	Jie et al.10	CTA/DSA	For hemoptysis	Common trunk at D12, RMA from right 4th intercostal artery	Horse shoe adrenals Isolated left gastric artery Ventrally placed aorta
5	Present case	Nadarajah et al.	CTA/DSA	Spinal Vascular malformation	Common trunk at L1 level RMA from left 9th intercostal artery	Horse show adrenals Filar AVF Dilated tortuous vessels in the rectum Retro-aortic left renal vein Ventrally placed aorta Isolated left gastric artery Sacral spina bifida Low-lying cord with fatty filum

CTA: Computed Tomography Angiography; DSA: Digital Subtraction Angiography; AVF: Arterio-Venous Fistula; MRA: Magnetic Resonance Angiography.

During early embryogenesis, following somatic organisation, mesodermal derivatives of dorsum of the entire embryo are supplied by a pair of dorsal aortae and its intersegmental arteries. At cervical level, on either side till C6 level, longitudinal anastomosis develops between these intersegmental arteries which form future vertebral arteries and most of their original connection with dorsal aorta disappears. Seventh intersegmental arteries on either side develop into subclavian arteries and supply developing limb buds. Caudal to it, usually two or three intersegmental arteries develop longitudinal anastomosis and forms future supreme intercostal artery, which is branch of costo-cervical trunk which in turn arise from the first part of subclavian artery. Dorsal aorta on the left side below the origin of seventh intersegmental artery develops into future proximal descending thoracic aorta, whereas the rest of the aorta develops from the fusion of bilateral dorsal aortae. The segment of unfused right dorsal aortae below seventh segmental artery and rostral to its fusion with left dorsal aorta usually disappears. Paired intersegmental arteries arising from dorsal aortae in thorax persist as thoracic intercostal arteries, whereas in abdomen they persist as lumbar arteries. Based on aforementioned embryological basis, it is difficult to explain the existence of the ACPIAT giving rise to intercostal arteries on either side. Brew et al.⁷ first reported this variant anatomy and Chang et al.⁸ proposed multiple hypotheses to explain its embryological basis. According to Brew et al.,⁷ ACPIAT could be

derived from, both dorsal aortae with its attached intersegmental arteries (or)from definitive aorta after the fusion of dorsal aorta (or) it may represent one dorsal aorta with its intersegmental arteries and transferred contralateral intersegment arteries from the other dorsal aorta which persist as definitive aorta (or) it may be derived from a longitudinal vessel other than the definitive aorta.

Chang et al.⁸ proposed persistence of vitelline circulation as the basis for this variant anatomy. Three out of four reported cases in literature^7,9,10 and our case showed that aortic segment supplying gut is seen ventrally placed and entering abdominal cavity through oesophageal hiatus, whereas ACPIAT is seen in expected normal location of aorta. Based on this observation, the hypothesis proposed by Chang et al. is more appropriate to explain this anatomical variant, as ventrally placed aortic segment could represent a persistent embryological vitelline arterial segment, whereas ACPIAT could be an hypoplastic aorta which contributes only to intercostal supply.

Interestingly, multiple associated congenital anomalies and variations that have been described in reported cases include kyphosis with multiple vertebral fusion anomalies, horse shoe adrenals, vaginal agenesis, pelvic kidney with renal artery originating form common iliac artery, isolated left gastric artery, replaced right hepatic artery, and isolated splenic artery^7–10 Our case also showed isolated left gastric artery, common left pulmonary venous trunk, horse shoe adrenals, defect in posterior elements of sacrum, low-lying tethered cord, fatty filum, filar AVF and rectal angiodysplasia. In view of multiple reported variations and anomalies, ACPIAT may represent part of much larger developmental defect in early embryogenesis which needs to be explored.

Although rare, knowledge about this entity is vital as ACPIAT may be the source of spinal cord supply. Inadvertent embolisation during endovascular treatment of spinal cord, vertebral vascular malformation and endovascular repair of aorta may lead to disastrous consequences if not recognised pre-operatively. Alternatively, ACPIAT may be a major non-bronchial feeder and source of haemorrhage in a patient with haemoptysis, hence prior knowledge of this entity by treating interventional radiologist will save invaluable time in emergency situation especially when expected feeders were not found.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Jeyaseelan Nadarajah https://orcid.org/0000-0003-2895-9267

Leve Joseph Devarajan Sebastian https://orcid.org/0000-0002-4777-2804