Right hand knob infarction

Abstract

A 69-year-old man presented at the ER with paresis of the left arm since one week. Except for hypertension and lumbosciatic pain, there was no past medical history. Clinical examination showed spontaneous pronation of the left forearm, decreased flexion of the left elbow and decreased dorsiflexion of the left wrist. Examination of the left hand revealed impossible flexion and extension of the fourth and fifth finger, impossible opposition of the fifth finger and decreased abduction of the third, fourth and fifth fingers. There were no sensory symptoms. There was a mild hyperreflexia of the left biceps tendon reflex. Coordination and muscle strength were normal in the left leg and on the right side of the body. Cranial nerves were normal as well. Non-contrast enhanced CT of the brain performed shortly after admission at the ER showed blurring and hypodensity of the grey–white matter of the right ‘‘hand knob’’ motor area. A 3T MRI of the brain with diffusionweighted sequences performed 3 days later confirmed the presence of a local infarction of the right cortical motor hand knob along with some additional smaller ischemic lesions in the right frontal and parietal lobes (Fig. 1). There was no evidence of hemorrhagic transformation on susceptibility weighted images. An MR angiogram of the neck showed a high-grade stenosis at both the proximal cervical and the cavernous segment of the right internal carotid artery. Monoparesis of the upper limb is an uncommon presentation of acute stroke with the two largest studies on the subject reporting prevalences of 2.6 and 0.7 %, respectively [1, 2]. In the acute phase these strokes can be very disabling, but most patients demonstrate a good functional long-term outcome [1, 2]. In the largest study to date on ischemic stroke presenting with isolated pure motor weakness of an upper extremity, the location of the infarcts uniformly involved the contralateral central sulcus region and the etiologies consisted of carotid artery disease (34 %), cardio-embolism (46 %) and small vessel disease (17 %) [2]. In most patients the motor hand area can easily be identified on CT and MR. The neural elements involved in motor hand function are located in a characteristic ‘‘precentral’’ knob, which most often has the form of an inverted omega (90 %) or a horizontal epsilon (10 %) when examined in the axial plane, and appears as a posteriorly directed hook (92 %) in the sagittal plane [3]. In our case, the hand knob had a horizontal epsilon shape on the right and an inverted omega shape on the left. This case emphasizes that the precentral ‘‘hand knob’’ can be easily identified in most patients and should be carefully inspected in patients who present with acute upper limb monoparesis. S. Dekeyzer M. Acou Department of Radiology and Medical Imaging, UZ Gent, De Pintelaan 185, 9000 Ghent, Belgium