Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 58, Num. 5, 2010, pp. 785-786

Neurology India, Vol. 58, No. 5, September-October, 2010, pp. 785-786

Letter to Editor

Corpus callosum infarct associated with combined variants in circle of willis

Elisabeth Andreadou¹, George K Papadimas¹, Nikolaos Sifakis², Constantinos Sfagos¹

¹ Department of Neurology, Athens National University, Aeginition Hospital, 74, Vas. Sophias Av. 11528 Athens, Greece
² Department of Nuclear Medicine, Alexandra Hospital Athens, Greece

Correspondence Address:
Elisabeth Andreadou
Department of Neurology, Athens National University, Aeginition Hospital, 74, Vas. Sophias Av. 11528 Athens
Greece
eandread@med.uoa.gr

Date of Acceptance: 17-Jul-2010

Code Number: ni10216

PMID: 21045514

DOI: 10.4103/0028-3886.72169

Sir,

A 46-year-old right-handed woman presented with a 3-week history of episodic failure to maintain right upper limb movement while performing routine tasks (i.e., washing the dishes), without weakness or impairment of consciousness . All the events occurred in the standing position and lasted for 5-10 min with no residual deficits. The last episode was also accompanied by involuntary sound repetition. Neurological examination was essentially normal. Interictal electroencephalography was also normal, excluding the possibility of simple partial seizures. Brain magnetic resonance imaging (MRI) revealed, on FLAIR and T2-weighted sequences, hyperintense lesions in the anterior portion of the corpus callosum (CC) extending to the right frontal and parietal lobes [Figure - 1]a-c. Given the age of the patient and the absence of vascular risk factors, demyelination was initially suspected. Callosal demyelinating lesions, however, are usually multiple, small, nodular and characteristically involve callosal-septal interface. Moreover, cerebrospinal fluid examination was normal with absence of oligoclonal bands. Furthermore, the concurrent MRI lesions were distributed only in the right hemisphere. Thus, the possibility of ischemic nature of the lesions was raised. Detailed cardiologic studies, including transesophageal echocardiogram and repeated Holter-electrocardiogram recordings, revealed no pathological findings suggestive of cardioembolism. MRI performed 15 days later showed subtle enhancement on the postcontrast T1-weighted images [Figure - 1]d. Digital subtraction angiography demonstrated an embryonic derivation of the right posterior cerebral artery (PCA) from the homolateral internal carotid artery (ICA) and a hypoplastic precommunicating part (A1) of the left anterior cerebral artery (ACA), with a patent anterior communicating artery (AComA) enabling blood supply from the right to the left ACA [Figure - 2]a and b. Tc-99m hexamethylpropyleneamine oxime (HMPAO) brain single photon emission computed tomography (SPECT) was subsequently performed to evaluate relative brain perfusion and assess whether this combination of developmental anomalies in the circle of Willis could predispose to infarction. It revealed decreased perfusion in the right parietal-frontal cortex and in the left posterior frontal cortex [Figure - 3], supporting our speculations. A follow-up MRI eight months later demonstrated old infarcts in the anterior portion of the body of the right CC and the right frontal and parietal lobes [Figure - 1]e-g. The patient remained stable during the 1-year follow-up, without neurological symptoms or signs.

Callosal infarcts are uncommon due to its rich blood supply by the ACA-PCA anastomotic complex and its resistance to small vessel ischemic disease. They usually extend to the neighboring structures and may present atypically with nonlocalizing signs and symptoms. ^[1] The patient's symptoms were compatible with right limb motor impersistence and transient stuttering, signs of callosal disconnection that more frequently develop after right hemispheric lesions. ^[2],[3] Given the unusual location of the infarct and the absence of source of embolism or factors predisposing to atherosclerosis, the rare combination of two anatomical variants of Willis circle ^[4] was postulated to be the underlying etiology. Developmental anomalies in the configuration and size of the cerebral arteries may predispose to cerebral ischemia, especially in young adults. The presence of fetal-type PCA increases the volume flow of the ICA. Moreover, absence of the A1 segment of ACA increases the flow rate of the contralateral ICA. ^[5] In our case, embryonic derivation of the right PCA combined with contralateral hypoplastic A1 might have further increased the volume flow of the right ICA, resulting in a disproportionately high workload of the vessel. Given the deficiency of collateral pathways, transient hypoperfusion, possibly attributed to blood pressure decreases after prolonged standing, might have resulted in hemodynamic failure in the right ACA territory and, consequently, in infarction. ^[6] This assumption is supported by the SPECT findings that revealed extensive hypoperfusion predominantly in the right hemisphere. In conclusion, although variations of the circle of Willis are common and usually asymptomatic, they may occasionally predispose to uncommonly located ischemic lesions by preventing the brain from sufficient collateral blood flow.

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