Journal of Neurology, Neurosurgery, and Psychiatry 1990;53:731-735 731 Infarction in the territory of the medial branch of the posterior inferior cerebellar artery Pierre Amarenco, Etienne Roullet, Marc Hommel, Pascal Chaine, Rene Marteau Department of Neurology, Hopital Saint-Antoine, Paris P Amarenco E Roullet R Marteau Department of Neurology, Hopital Lariboisiere, Paris, France P Chaine Department of Neurology, Hopital Nord, Grenoble, France M Hommel Correspondence to: Dr P Amarenco, Service de Neurologie, H6pital SaintAntoine, 184 rue du Fg StAntoine, 75571 Paris cedex 12, France. Received 10 August 1989 and in revised form 11 December 1989. Accepted 3 January 1990 makes a third loop. The common trunk gives Abstract We report 10 cases of cerebellar infarc- rise to a medial branch (mPICA) and a lateral tion in the territory of the medial branch branch at a variable level between the two first of the posterior inferior cerebellar loops.'2 13 From pathological data, on an axial artery (mPICA). Axial sections on MRI mid-medullary and cerebellar section, the through the middle of the medulla and mPICA supplies a triangular area with a dorthe cerebellum showed the infarction as sal base and a ventral apex towards the fourth a triangular area with a dorsal base and ventricle (fig 2).'4 The medial branch of the a ventral apex directed towards the PICA supplies the inferior vermis (nodulus, fourth ventricle. The infarct also uvula, pyramis, tuber and sometimes clivus) involved the lateral and dorsal medulla and the internal parts of the lobulus semilunwhen the mPICA supplied all or part of aris inferior, lobulus gracilis and tonsil; these regions. Three clinical patterns mPICA exists even when the PICA is hypowere observed: 1) pseudolabyrinthine plastic. The usual lateral branch of the PICA signs with or without dysmetria and arises, in this instance, from the anterior and ataxia when the medulla was spared; inferior cerebellar artery,'5 as there is a marked axial lateropulsion was present reciprocal relation between these two arteries. in most cases; 2) complete or incomplete At times the sole medial branch participates in Wallenberg's syndrome, when the the blood supply of the medulla'0 in its dorsal medulla was involved; 3) silent infarc- region, and sometimes in the lateral retrotion. These syndromes are precisely olivary area.2 This latter region is usually those previously attributed to PICA supplied by small short circumferential occlusion without distinction of the arteries arising from the vertebral artery.' 16 17 branch involved. No alteration of cons- No correlations between these pathological ciousness was recorded and spontaneous data and brain imaging are available. recovery was the rule. Cerebellar infarction in the distribution of the mPICA can be regarded as a benign condition Patients and methods Ten cases of cerebellar infarction involving with a good prognosis. the territory of the mPICA were observed The posterior inferior cerebellar artery from 1986-89. In all but one (case 7) the (PICA) sometimes supplies the lateral diagnosis of cerebellar infarction had been medullary area.'2 Its occlusion may then made or suspected on clinical grounds and result in Wallenberg's syndrome.34 When the imaging studies showed involvement of the PICA does not supply the medulla, its medial part of the caudal cerebellum. Cases occlusion may lead to a pure vertigo, with or showing abnormality in a larger region than without associated cerebellar signs.9 Syn- the territory of the medial branch, that is, *dromes resulting from the occlusion of the medial or the lateral branch of the PICA have been clarified only in necropsy studies by Goodhart et al "' and Amarenco et al." Given the good prognosis of these infarcts, however, clinico-pathological data may not reflect the true clinical spectrum, necessitating clinicoradiological studies. Computed tomography (CT) and magnetic resonance imaging (MRI) of 10 examples of infarction in the territory of the medial branch of the PICA gave us an 4 opportunity for clinico-anatomical correlation. After arising from the vertebral artery, the PICA courses transversely and downward along the medulla. It then makes a first caudal 2 loop, ascending in the sulcus separating the 1 Anatomical Figure drawing of the most frequent dorsal medulla from the tonsil of the course the of posterior inferior cerebellar artery (PICA) cerebellum (fig 1). It then makes a second loop and its two main branches. 1, PICA; 2, lateral branch of above the cranial part of the tonsil and des- PICA; 3, medial branch of PICA; 4, internal part of the cends, following the inferior vermis, where it cerebellar hemisphere; 5, vermis; 6, cerebellar tonsil. Amarenco, Roullet, Hommel, Chaine, Marteau 732 3 Figure 2 Anatomical drawing of the territory of the medial branch of the posterior inferior cerebellar artery (mPICA). 1, cerebellar tonsil; 2, lobulus semilunaris inferior; 3, vermis (pyramis); 4, territory of mPICA; 5, lobulus gracilis; 6, lobulus biventer. Modified from Amarenco et al". were flexor. Repeated CT scans were normal. MRI, 42 days after onset, showed infarction in the right mPICA territory (fig 4). ECG, echocardiography and ultrasonography of extracranial arteries were normal. On day 13 he became severely confused but this resolved with the correction of moderate hyponatraemia. Three months after the onset the only sequelae were a slightly unsteady gait, right beating horizontal nystagmus and facial pains. Case 10 was a 55 year old diabetic and hypertensive man who noticed the sudden onset of vertigo (preventing him standing) with dysarthria, nausea and a feeling of imminent death. On admission, two days later, postural vertigo and unsteadiness of gait had persisted. Examination showed right tonic past pointing and left beating horizontal nystagmus. There was neither dysmetria, motor weakness, sensory impairment nor cranial nerve dysfunction. CT and MRI showed infarction in the right involving the whole territory of the PICA, were excluded. Two cases were proven by CT and eight by MRI. Case 7 was selected on the same radiological criteria without related symptoms or signs. Angiography was performed in only one patient. Cases 8 and 9 were included in the series by Hommel et al.'8 Results Case 3 was an 80 year old hypertensive woman who experienced the sudden onset of vertigo, posterior headache and palpitations. On admission, six hours after the onset, her blood pressure was 160/80. The pulse was 115 and irregular. The vertigo worsened with head movement and improved on recumbency. There was dysmetria of the left superior limb and gaze deviation to the left. Saccades to the right were absent, but oculocephalic responses were preserved. The rest of the neurological examination was normal. A CT head scan was normal. The next day, a T2-weighted MRI showed increased signal in the territory of the left mPICA, sparing the brain stem (fig 3). An electrocardiogram (ECG) showed atrial fibrillation. Echocardiography was normal. The vertigo disappeared a few days later but the patient needed assistance when standing up and walking because of severe axial lateropulsion to the left. Twenty days after the onset of the symptoms the patient was discharged. She was able to walk by herself, ipsilateral gaze and axial lateropulsions had disappeared, but disorders of pursuit eye movements were recorded.'9 Case 5 was a 76 year old hypertensive man who experienced the sudden onset of vertigo, headache, nausea and difficulty in swallowing. There was right hemiparesis and facial palsy, which lasted a few hours. On admission the next day he had hiccoughs and on the right side dysmetria, paralysis of the ninth and tenth cranial nerves, and hypoaesthesia of the face. There was neither weakness, sensory signs on the left side, oculomotor disturbance or impaired consciousness. Plantar responses Figure 3 Case 3: Infarction involving the territory of the medial branch of the left PICA in isolation (a,b,c), with a characteristic triangular shape on section through the medulla (b) Infarction in the territory of the medial branch of the posterior inferior cerebellar artery Figure 4 Case 5: Right triangular high signal on T2weighted MRI axial section of the caudal cerebellum. 733 complete Wallenberg's syndrome was observed in three patients. In six patients there were no signs of medullary involvement; they showed vestibular signs (6), axial lateropulsion (5) or dysmetria (4), either isolated or in association. Silent infarction had occurred in one patient. On axial MRI sections through the midmedulla, the cerebellar territory of mPICA has a triangular shape (fig 3 to 6) and to a larger extent in the lower sections of the cerebellum as shown in case 3 (fig 3a, b, c). Case 8 illustrates an anatomical deviation whereby the contralateral mPICA supplies the vermis and the lobulus semilunaris inferior, taking over the most medial part of the territory usually supplied by the ipsilateral mPICA.'41820 A good quality CT scan may be necessary to show infarction of this territory illustrated in cases 1, 2 and 10 (fig 6). Infarction was probably due to cardiac embolism in three cases: two had paroxysmal and one chronic atrial fibrillation. Angiography (one case) showed occlusion of the right mPICA after its second loop (Fig 5c) due to either atherosclerotic or cardiac embolism. The stroke mechanism remained undetermined in six other cases. mPICA territory (fig 5). Angiography showed an occlusion of the right mPICA after its second loop (Fig 5c) as well as severe atherosclerosis of the end of the vertebral arteries and of the basilar artery. The patient spontaneously improved and three weeks after the onset was discharged with residual intermittent dizziness only. Symptoms and signs of the 10 cases are summarised in table 1. Symptoms included vertigo (8), nausea or vomiting (8), headache (5) and inability to walk (2). No patient had Discussion alteration of consciousness, and spontaneous To our knowledge there are no reports concerimprovement occurred in all cases. Partial or ning the territory of the mPICA on MRI,2' nor h. .. . . . a. i ; !;I . .;|IIe ,i ; : Amarenco, Roullet, Hommel, Chaine, Marteau 734 Table Infarcts of the medial branch of the posterior inferior cerebellar artery Author, year Age, sex Symptoms at onset Signs Source diagnosis Goodhart et al, 1936 (Case 1) Fisher et al, 1963 (Case 2) Duncan et al, 1975 (Case 1) Amarenco et al, 1989 (Case 6028) (Case 5193) (Case 4001) 64/Male Dizziness, inability to walk Wallenberg's syndrome Necropsy 66/Female 78/Male Necropsy finding Vertigo Nystagmus Necropsy Necropsy 78/Male 53/Male 71/Male (Case 4419) (Case 6219) (Case 4417) (Case 3399) (Case 3368) (Case 5705) Present series (Case 1) 61/Female 74/Male 58/Female 66/Female 64/Male 75/Male Vertigo Wallenberg's syndrome Vertigo, vomiting Wallenberg's syndrome Vertigo, vomiting, headache, inability to walk Wallenberg's syndrome Vertigo, facial numbness Wallenberg's syndrome Vertigo Overshadowed by other neurological disorder Overshadowed by other neurological disorder Necropsy finding Necropsy finding 43/Male (Case 2) (Case 3) 78/Male 80/Female (Case 4) 73/Female (Case 5) 76/Male (Case 6) 25/Male (Case 7) (Case 8) (Case 9) 45/Female 51/Female 57/Male (Case 10) 55/Male Vertigo, vomiting, headache, inability to walk Inability to walk Vertigo, vomiting, posterior headache Vertigo, vomiting, posterior headache Vertigo, vomiting, posterior headache Vertigo, vomiting, posterior headache MRI finding Vertigo, vomiting Vertigo, vomiting, posterior headache Vertigo, nausea, dysarthria of any case with anatomical demonstration of mPICA occlusion and corresponding infarction. Goodhart and Davison'° reported a case of infarction in the dorsal area of the medulla, without involvement of the cerebellar lobules, but described mPICA occlusion as "incomplete". In a pathological study of 28 cases of infarction in the territory of the PICA" two of the authors of this study observed nine cases with infarction of the medial part of the caudal cerebellum in a triangular pattern, consistent with the anatomical distribution of the mPICA;20 there were, however, no cases with mPICA occlusion. Angiographic confirmation of mPICA occlusion was shown in one case of the present series (case 10, fig 5c). Our MRI and CT anatomical findings correlate well with the pathological data previously reported." It may therefore be assumed that the arterial territory involved in our 10 cases was that of the mPICA, with its typical triangular shape (fig 2). Ipsilateral axial lateropulsion, mild dysmetria Ipsilateral axial lateropulsion Ipsilateral axial lateropulsion, mild dysmetria, gaze deviation Ipsilateral axial lateropulsion, mild dysmetria Incomplete Wallenberg's syndrome Ipsilateral axial lateropulsion, dysmetria Necropsy Necropsy Necropsy Necropsy Necropsy Necropsy Necropsy Necropsy Necropsy CT CT MRI MRI MRI MRI Wallenberg's syndrome Wallenberg's syndrome MRI MRI MRI Unilateral vestibular syndrome MRI Table 1 compares the symptoms and signs observed in our patients with those of the pathological reports of infarctions in the mPICA territory from the literature.'51011 Cases with Wallenberg's syndrome were less frequent in the present series than cases without signs of medullary involvement. Vertigo and vestibular signs were the most prominent clinical features. At times they occurred alone mimicking a labyrinthine lesion, as previously reported.569 " In each of these cases, however, there was at least one symptom or sign which led to the diagnosis such as posterior headache, slight dysarthria or horizontal (rather than horizonto-rotatory) nystagmus. Normal caloric responses and direction-changing nystagmus on gaze to each side or after changing the posture of the head or decubitus are two other signs which have been described in "pure" vestibular involvement of PICA infarcts.58 The most striking clinical finding was an axial lateropulsion which prevented orthostatism and persisted long after the disappearance of the tonic vestibular deviation. In our case 2 it was isolated. In case 3 an ipsilateral lateropulsion of gaze was added to vertigo and axial lateropulsion. In all cases it was the last sign to improve. Such a lateropulsion has been observed in lesions involving thalamus,2 medulla2' or the anterolateral part of the rostral cerebellum.2"26 Figure 6 Case 1: Low density area on CT lying in the territory of the mPICA. Thus two clinical patterns can be distinguished. 1) First, Wallenberg's syndrome, which occurs when medullary signs overshadow cerebellar signs. This occurs when the mPICA supplies all or part of the lateromedullary territory. It has been estimated that an infarction in the territory of the mPICA occurs in 13o% of Wallenberg's syndrome." 2) Secondly, Infarction in the territory of the medial branch of the posterior inferior cerebellar artery a syndrome consisting of vertigo, vestibular signs, dysmetria, ataxia, and axial lateropulsion, isolated or in association, which occurs when the medulla is spared. These two syndromes have been previously attributed to occlusion of the main trunk ofthe PICA.45 Our findings suggest that they could be due to the sole occlusion of the medial branch of the PICA. However, silent infarct (present in five out of the 12 pathological cases and one out of our 10 patients) may also occur. No differences were found in brain imaging between the two clinical patterns and the case with silent infarct. In two of the three infarcts with Wallenberg's syndrome, MRI showed a lateral medullary infarct. On the other hand, the clinical syndromes resulting from occlusion of the lateral branch of the PICA are not known. No clinical reports are available in the literature. Two pathological series relating to infarction in the PICA territory and its branches reported six cases of involvement of the lateral branch of the PICA (case 4 from Goodhart et al " and five cases from Amarenco et al "). All cases were confounded by other neurological disorders or were chance necropsy findings. This suggests that the involvement of this part of the cerebellum may be clinically silent. Our series also points out that embolism is a not uncommon cause." Neither hydrocephalus nor fatal outcome occurred. This could be explained by the small territory supplied by the mPICA, that is, by the small extent of the resulting infarction. According to Sypert and Alvord27 more than one third of the cerebellum must be involved by the infarct before oedema leads to coma and death. Thus, cerebellar infarction in the distribution of the mPICA may be regarded as a benign condition with a good prognosis. We are indebted to Professor J Lapresle and to Dr D Malapert for permission to use clinical data from their patients (cases 1 and 7) and Doctor Bryan Youl for his invaluable help with the English. 1 Fisher CM, Karnes WVE, Kubick CS. Lateral medullary infarction: the pattern ofvascular occlusion. 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