―Case Reports― An Isolated Unilateral Pontomedullary Lesion Due to An Intracranial Dural Arteriovenous Fistula Mimicking A Brain Tumor - Case and Review Pei-Ya Chen１, Yu-Hsiu Juan２,3 and Shinn-Kuang Lin１,3 1 Stroke Center and Department of Neurology, Taipei Tzu Chi Hospital 2 Department of Radiology, Hualien Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taiwan 3 School of Medicine, Tzu Chi University, Hualien, Taiwan Intracranial dural arteriovenous fistula (DAVF) with perimedullary venous drainage may cause brainstem swelling and represent a diagnostic challenge. A 66-year-old man presented to the emergency room with recurrent vertigo, minimal truncal ataxia with a wide-based gait, and a slightly impaired tandem gait. Brain magnetic resonance imaging (MRI) revealed a hyperintense lesion in the left pontomedullary area on T2-weighted images (T2WIs) with partial gadolinium enhancement, but without increased signals on diffusion-weighted images. Abnormal serpentine flow void vessels surrounding the medulla and upper cervical spinal cord were initially overlooked but discovered later. An angiogram revealed DAVF with feeders from the right occipital artery and the meningeal branch of the right distal vertebral artery with drainage into the anterior medullary venous system and the perimedullary veins. The patient underwent a successful transarterial endovascular embolization and improved gradually. A brain MRI at 3-month follow-up revealed a residual hyperintense signal on the T2WIs in the left lower medulla. Six cases of patients exhibiting DAVF with isolated unilateral brainstem swelling from the literature were reviewed. Isolated unilateral brainstem swelling due to intracranial DAVF with perimedullary venous drainage is extremely rare and might mimic a tumor on MRI. Abnormal serpentine flow void vessels on the surface of the brainstem or spinal cord are crucial diagnostic clues. (J Nippon Med Sch 2019; 86: 48―54) Key words: brainstem swelling, dural arteriovenous fistula, perimedullary venous drainage, venous congestion Introduction presentation of 89% and an estimated annual risk of Dural arteriovenous fistulas (DAVFs) are abnormal con- hemorrhage of 10%2,4. Intracranial DAVF with perimedul- nections between small arterial and venous systems with- lary drainage (Cognard Type V) may cause brainstem 1 out intervening capillary beds . Intracranial DAVF is rare, dysfunction or cervical myelopathy due to swelling or and is estimated to account for less than 10% of cerebral ischemia of the corresponding structures. However, early vascular malformations2. The clinical symptoms of intrac- diagnosis of DAVF is challenging. The hallmark of di- ranial DAVFs are mainly related to the locations of ve- lated perimedullary veins caused by venous congestion nous drainage, with the most aggressive presentation be- in the DAVF usually presents as serpentine flow void le- ing intracranial hemorrhage or neurological deficits2,3. sions around the brainstem or spinal cord. However, they The two most widely used grading systems, according to may be too subtle to be observed or even absent in a the complicated venous drainage patterns, were devised magnetic resonance imaging (MRI) study. Delayed diag- 4,5 by Cognard and Borden . High-grade DAVFs (Cognard nosis might cause unpredictable complications. Type III-V with venous cortical or perimedullary drain- Herein, we present a rare case of intracranial DAVF age) have an estimated incidence of aggressive clinical with perimedullary drainage that presented as recurrent Correspondence to Shinn-Kuang Lin, MD, Department of Neurology, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, No. 289 Jian Guo Road, 231, Xindian district, New Taipei City 23142, Taiwan E-mail: stuartlin0428@gmail.com, sk2022@tzuchi.com.tw Journal Website (http://www2.nms.ac.jp/jnms/) 48 J Nippon Med Sch 2019; 86 (1) Pontomedullary Lesion Due to Dural Arteriovenous Fistula Fig. 1 Brain computed tomography indicates normal results (A, B). T2-weighted images from brain magnetic resonance imaging (C, D) depict a hyperintense swelling lesion at the left pontomedullary area (large arrows). The lesion presents a normal signal on the diffusion-weighted images (E), a slightly high value on the apparent diffusion coefficient map (F), and a partial enhancement on the T1-weighted image (arrowhead in G). Brain magnetic resonance angiography reveals normal intracranial vessels (H). Abnormal serpentine flow void lesions are present at the surface of the medulla and upper cervical spinal cord (small arrows in C, D). vertigo and very mild unsteady gait. The appearance of (Fig. 1A, B). A brain MRI study revealed a hyperintense isolated unilateral pontomedullary swelling with en- lesion at the left lower pons and medulla oblongata on T hancement in MRI mimicked a tumor. Further angiogra- 2-weighted images (T2WIs) without increased signals on phy confirmed the diagnosis and subsequent endovascu- diffusion-weighted images (DWIs), but a slightly high lar treatment completely eliminated the symptoms. value on the apparent diffusion coefficient (ADC) map (Fig. 1C-F). The lesion exhibited partial gadolinium en- Case Presentation hancement on T1-weighted images (Fig. 1G). Magnetic A 66-year-old man, without hypertension, diabetes, or a resonance angiography (MRA) did not reveal a promi- history of head injury, had an acute onset of dizziness, nent atherosclerotic change in the intracranial arteries vertigo, and unsteady gait 2 days prior to visiting the (Fig. 1H). An acute brainstem infarct was excluded from emergency room. He had a history of an operation and the findings of the MRI study. However, vasogenic radiotherapy for small cell lung cancer 11 years previ- edema from an inflammatory, infectious, or neoplastic ously. He did not complain of any associated nausea, process was considered due to the similar MRI patterns. vomiting, double vision, slurred speech, swallowing dis- The laboratory studies revealed a slightly elevated fast- turbance, or limb weakness. He had a similar episode of ing glucose and low-density lipoprotein, but normal he- vertigo with unsteady gait and had visited another hos- mogram and antinuclear antibodies. A tumor marker sur- pital approximately 1 month previously. A carotid vey based on the patient’s history of lung cancer, includ- sonography study at that time indicated a mild athero- ing squamous cell carcinoma antigen, tissue polypeptide matous lesion. His symptoms of dizziness and vertigo antigen, carcinoembryonic antigen, cancer antigen 15-3, improved several days later but he still felt a slightly un- carbohydrate antigen 19-9, and prostate specific antigen, steady sensation when walking. A neurological examina- revealed normal results. A cerebrospinal fluid analysis tion on admission revealed truncal ataxia attenuated on demonstrated an elevated total protein level of only 100 the left side, a very mild wide-based gait, and a slightly mg/dL with normal results for cell counts, cryptococcal impaired tandem gait. Brain computed tomography (CT) antigen, and viral immunological values. at the emergency room did not indicate any abnormality J Nippon Med Sch 2019; 86 (1) A carotid and transcranial duplex sonographic study 49 P. Chen, et al Fig. 2 Anterior (A), lateral (B), and oblique (C) views in a right external carotid artery (ECA) angiogram, depicting a dural arteriovenous fistula (DAVF) with a feeder with fistulous point from the occipital artery (small arrows) that drains into the perimedullary veins, with reflux into the pontomesencephalic, left transverse pontine, and left anterolateral pontine veins (arrowheads in A), as well as the anterior medullary venous system (arrowheads in C). Anterior (D) and lateral (E) views in a vertebral artery (VA) angiogram, revealing a DAVF with a feeder from the meningeal branch of the right VA (small arrow) that drains into the anterior and posterior perimedullary veins (arrowheads). Oblique view (F) in a right ECA angiogram, revealing the disappearance of DAVF after embolization therapy with the Onyx-18 solution (large arrow). revealed a mild atheromatous lesion in the right carotid system, thus causing venous congestion and edema of bifurcation with normal flow velocities, flow resistances, the left lower pons and medulla. and flow volumes in the bilateral common carotid arter- The patient underwent a transarterial endovascular ies, internal carotid arteries, external carotid arteries embolization using a right femoral artery approach with (ECAs), vertebral arteries (VAs), occipital arteries, and a 6-French Neuron guiding catheter (Penumbra Inc, San posterior auricular arteries. Neither engorgement nor Leandro, California, USA) and a microcatheter (Apollo, pulsatile retrograde flow was observed in the bilateral ev3-Covidien, Irvine CA, USA), under general anesthesia. superior ophthalmic veins. A brainstem biopsy was con- The embolization of the AVF was performed via the su- sidered for a pathological diagnosis. However, a detailed perselective right occipital artery with injection of Onyx- review of the MRI images with radiologists discovered 18 an abnormal serpentine flow void at the ventral surface into the feeder branch (Fig. 2F). After embolization, the (3 mL; ev3-Covidien, Irvine CA, USA) in 10 min of the medulla (Fig. 1C) and along the anterior and pos- patient’s symptoms improved gradually and no further terior surfaces of the upper cervical spinal cord (Fig. 1D). vertigo or ataxia occurred. A brain MRA at 3-month A further angiography study revealed DAVF with a main follow-up revealed that the serpentine flow void at the feeder from the right occipital artery and a minor feeder medulla and cervical spinal cord had disappeared and from the meningeal branch of the right distal VA (Fig. 2 that the edematous change of the left lower pons and A-E). The fistula drained into the anterior and posterior medulla had considerably improved with a residual hy- perimedullary veins with reflux into the pontomesen- perintense signal on the T2WI at the left lower medulla cephalic, left transverse pontine, and the left anterolateral (Fig. 3). pontine vein as well as the anterior medullary venous 50 J Nippon Med Sch 2019; 86 (1) Pontomedullary Lesion Due to Dural Arteriovenous Fistula Fig. 3 Follow-up brain magnetic resonance imaging after 3 months revealed the disappearance of the serpentine flow void lesion with a residual hyperintense signal on the T2-weighted images at the left lower medulla. Discussion than a brain CT for the study of acute lesions involving Our patient experienced recurrent acute dizziness and the posterior fossa or brainstem. Common causes of the vertigo with an unsteady gait during a 1-month period. hyperintense lesions on T2WIs in an MRI study include No other neurological deficit was reported except for infarction, inflammation, infection, demyelination, tumor, subtle cerebellar signs presenting as minimal truncal and vasogenic edema6. The most common vascular cause ataxia and a slightly impaired tandem gait. Although the for a hyperintense lesion on T2WIs is an acute cerebral brain CT study revealed a normal result, a further brain infarct, which also causes an increased signal on DWIs MRI study revealed an edematous lesion at the left lower but a decreased signal on the ADC map. An acute cere- pons and medulla oblongata. However, the abnormal ser- bral infarct was excluded quickly from the MRI results in pentine flow void vascular structures around the lower this patient due to a normal signal on DWIs and a brainstem and upper cervical cord were overlooked in- slightly high value on the ADC map. Decision-making itially. No other inflammatory, infectious, or neoplastic for further surveys of unilateral hyperintense lesions on process was observed after serial studies. Abnormal ser- T2WIs is difficult. Noninvasive laboratory studies were pentine flow void vessels discovered during the subse- unable to identify the possible pathological correlation. quent careful review of the MRI images raised the suspi- Similar to venous sinus thrombosis, DAVF is a critical cion of DAVF. The cerebral angiography confirmed the fi- vascular cause of brain edema from venous congestion. nal diagnosis of intracranial DAVF and the patient re- In contrast to cytotoxic edema in an acute infarct with an ceived successful endovascular treatment. increased intracellular fluid and a low ADC value, vaso- Recurrent acute vertigo with unsteady gait may origi- genic edema is associated with an increase of extracellu- nate from a peripheral or central source. When no or lar fluid and might cause a high ADC value in an MRI negligible brainstem or cerebellar signs are observed, study7. A tumor-mimicking brainstem edematous lesion these sources are difficult to differentiate, particularly has been emphasized to distinguish vasogenic edema of when severe vertigo and vomiting interferes with a the brainstem from DAVF1,8. Careful interpretation of the proper neurological examination during the acute stage. MRI images for the abnormal serpentine flow void vas- For our patient, a neurological consultation in the emer- cular structures is crucial for the recognition of DAVF. gency room enabled the detection of these subtle cerebel- However, studies have reported brainstem swelling from lar signs. Otherwise, this patient may have been dis- DAVF without adjacent abnormal serpentine flow void charged from the emergency room based on a normal vascular structures, either due to small shunting or dis- brain CT study, an absence of prominent stroke risk fac- tant spinal DAVF6,8. In Haryu’s review, the presence of tors, and the partial relief of symptoms after treatment, perimedullary flow-related signal voids was detected in similar to his episode 1 month previously. only 37% of patients with Cognard Type V DAVF9. How- A brain MRI study provides much more information J Nippon Med Sch 2019; 86 (1) ever, Roelz et al suggested that combining contrast51 P. Chen, et al enhanced MRI and MRA might increase the detection isolated unilateral brainstem lesion due to DAVF have rate to 85%6. A “black butterfly” sign, due to hemorrhage been reported in studies in the English language litera- caused by prolonged venous congestion, on T2*- and ture6,8,13,14,16. A summary of these 6 cases is presented in Ta- susceptibility-weighted MRI in the dorsal aspect of the ble 1. Nausea, vomiting, and vertigo, which represent a medulla and the central gray matter of the cervical spinal vestibular dysfunction, were the most common initial cord has been reported to facilitate the diagnosis of symptoms in these 6 patients. However, all the patients DAVF10. except for the present patient had other coexisting brain- Intracranial DAVFs have a wide range of presentations, stem signs such as motor deficits, bulbar dysfunction, or including pulsatile tinnitus, acute subarachnoid hemor- Horner syndrome. The ECA and VA were the most com- rhage, brainstem dysfunction, myelopathy, radiculopathy, mon feeders of the DAVF. All patients received endovas- neuralgia, cranial palsy, and seizure. Neurological symp- cular treatment. Two patients received further surgical toms correlate with the location and severity of venous treatment. All the patients exhibited clinical improve- drainage3,7. Male patients might have more aggressive ment, and 2 patients had a complete regression of symp- symptoms, such as hemorrhage due to more frequent toms. In the present case, most shunting flows drained cortical venous drainage4. The clinical presentation and from the right occipital artery into the anterior perime- classification of DAVF are chiefly based on its venous dullary veins with reflux into the pontomesencephalic, drainage pattern. According to the Cognard classification, left transverse pontine, and the left anterolateral pontine the DAVF in our patient was classified as a Type V fis- veins. The unstable shunting pressure with hemody- tula, which is characterized by perimedullary venous namic stress resulted in focal venous congestion causing 4 drainage . This type of DAVF may also be classified as isolated edema of the left lower pons and medulla with craniocervical junction, infratentorian, or posterior fossa recurrent brain stem dysfunction symptoms. The revers- 11―13 . Progressive ible edematous left pontine lesion improved after the em- myelopathy or brainstem dysfunction occurs due to an bolization of the shunting from the right occipital artery edematous or ischemic change in the cervical spine or and, thereafter, no clinical symptoms were observed. DAVF according to its specific location brainstem caused by venous congestion with high ve- Carotid duplex sonography has been recommended as nous pressure in the pontomesencephalic vein, anterior the initial screening tool for diagnosis and follow-up in medullary venous system, and perimedullary veins. patients exhibiting symptoms related to intracranial Typically, the MRI images of patients with Cognard Type DAVF17. The parameter of resistance index of the ECA V DAVF reveal centrally located medullary or pontome- (cutoff points: right, 0.72; left, 0.71) yielded an 84% accu- dullary edema, with various degrees of cervical spinal racy for predicting DAVF. However, small arteriovenous 6 cord involvement . Isolated brainstem swelling without shunting with slow flows may not be detected by using spinal cord involvement is uncommon7,14,15. Asri et al re- ultrasound. We did not observe any abnormal flows or viewed 58 patients who had intracranial DAVF with pe- resistance indexes in the bilateral ECAs, VAs, or even oc- rimedullary venous drainage (Cognard Type V) from cipital arteries through carotid duplex sonography in our 3 1988 until 2011 . Swelling changes involving both the patient. Digital subtraction angiography remains the gold brainstem and spinal cord, and involving the spinal cord standard for the diagnosis and evaluation of DAVF. A 6- alone were observed in 52% and 44% of patients, respec- vessel angiography, including bilateral internal carotid tively. Only 2 patients had isolated brainstem swelling in arteries, ECAs, and VAs, with appropriate selective arte- the MRI studies. Furthermore, isolated unilateral brain- rial angiography, is necessary for a comprehensive sur- stem swelling without spinal cord involvement is ex- vey of such complicated arteriovenous fistulae. An endo- tremely rare and more difficult to distinguish from other vascular approach through a super-selective transarterial pathological conditions. Roelz et al also reviewed 58 re- embolization of the feeders with Onyx has become the ported cases of intracranial DAVF with perimedullary mainstay of therapy. Transvenous embolization, surgery, spinal venous drainage from 1992 to 2014 and revealed and stereotactic radiosurgery may be adjunctive treat- that only 3 patients (7%) had a unilateral brainstem le- ments to transarterial embolization18. sion6. We conducted a review and discovered 2 more pa- Most of the reported instances of brainstem edema re- tients with a unilateral brainstem lesion reported by solved gradually after successful obliteration of the Probst et al in 1994 and by Duan et al in 20178,13. Includ- DAVF. A residual brainstem lesion and neurological defi- ing the patients mentioned here, only 6 patients with an cits might be present in patients with brainstem ischemia 52 J Nippon Med Sch 2019; 86 (1) J Nippon Med Sch 2019; 86 (1) due to cytotoxic edema. The early recognition and proper treatment of DAVF is crucial to prevent extensive damICA: internal carotid artery, ECA: external carotid artery, MMA: middle meningeal artery, OA: occipital artery, APA: ascending pharyngeal artery, PAA: posterior auricular artery Complete regression of symptoms Improved Improved Improved Left sigmoid sinus, pontomesen- Endovascular cephalic vein, anterior and posterior perimedullary veins Lateral medullary vein, anterior Endovascular perimedullary/perispinal veins and surgical right superior petrosal sinus, peri- Endovascular medullary vein Anterior medullary veins, anterior Endovascular and posterior perimedullary veins Left pontomedullary Right pontomedullary Right MMA, to cerebellar peduncle OA, APA, PAA Right pons Right MMA, Right cerebellum OA Left pontomedullary Right OA, VA Improved Left transverse-sigmoid sinus and Endovascular spinal perimedullary veins Left MMA, OA, APA, ICA, right VA Left OA Right medulla Complete ression of symptoms Endovascular and surgical Right transverse sinus Right pons, right thala- Right ICA, mus, right cerebellum right ECA 40/F Probst et al. 199413 Headache, nausea, vertigo, disorientation, somnolence, dysarthria, ataxic gait, bilateral positive Babinski signs Satoh et al. 38/F Nausea, vomiting, vertigo, nystagmus, swal200514 lowing difficulties, right Horner syndrome, mild right hemiparesis Sugiura et al. 69/F Nausea, vomiting, nystagmus, left Horner 200916 syndrome, swallowing difficulty, mild right lower limb weakness, left cerebellar ataxia 76/M Nausea, vomiting, blurred vision, dysphaRoelz et al. gia, right ptosis, truncal and limb ataxia 20156 Duan et al. 67/F Headache, confusion, somnolence, bilateral 20178 hemiparesis with positive Babinski signs Present case 66/M Nausea, vomiting, vertigo, truncal ataxia Venous drainage Arterial source Location of swelling Symptoms/signs Age/ gender Reference Table 1 Reported cases of isolated unilateral brainstem swelling due to intracranial dural arteriovenous fistulae Treatment Outcome Pontomedullary Lesion Due to Dural Arteriovenous Fistula age and subsequent hemorrhage. For our patient, a residual high-intensity lesion remained at 3-month follow-up in the left lower medulla, which was apparently caused by a small residual shunt from the meningeal branch of the right VA. However, no clinical symptoms were observed. Regular follow-up MRI studies are necessary to assess the development of new symptoms or the progression of residual DAVF. In conclusion, isolated unilateral brainstem edema without spinal cord involvement due to intracranial DAVF with perimedullary venous drainage is rare and might mimic a brainstem tumor in an MRI study. Abnormal serpentine flow void vascular structures on the surface of the brainstem or spinal cord are crucial diagnostic clues. Early identification and proper treatment of DAVF usually leads to favorable clinical outcomes. Acknowledgements: The study was supported by grants from Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation (TCRD-TPE-105-12). 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