During chick limb development, the Abd-B subfamily of genes in the HoxA cluster are expressed in a region-specific manner along the proximodistal axis. To elucidate the function of Hoxa-13 that is expressed in the autopod during normal limb development, Hoxa-13 was misexpressed in the entire limb bud with a replication-competent retroviral system. Misexpression of Hoxa-13 resulted in a remarkable size reduction of the zeugopodal cartilages as a result of the arrest of cartilage cell growth and differentiation restricted in the zeugopod. This size reduction seems to be attributable to homeotic transformation of the cartilages in the zeugopod to the more distal cartilage, that of the carpus/tarsus. This transformation was specific to Hoxa-13 and was not observed by overexpression of other Hox genes. These results indicate that Hoxa-13 is responsible for switching the genetic code from long bone formation to short bone formation during normal development. When the limb mesenchymal cells were dissociated and cultured in vitro, Hoxa-13-expressing limb mesenchymal cells reassociated and were sorted out from nonexpressing cells. Forced expression of Hoxa-13 at the stage that endogenous Hoxa-13 was not expressed as of yet altered the homophilic cell adhesive property. These findings indicate the involvement of Hoxa-13 in determining homophilic cell-to-cell adhesiveness that is supposed to be crucial for the cartilage pattern formation.

The authors report a case of a myxoid chondrosarcoma of the pineal region in a 37-year-old woman who presented with an intratumoral hemorrhage. Partial removal of the tumor in an initial surgery resulted in failure to establish a definitive diagnosis. The residual tumor enlarged after a second intratumoral hemorrhage 14 months after the onset of the first symptoms, and gross-total resection of the tumor was achieved in a second surgery. Histological and immunohistochemical findings after the second surgery were consistent with a diagnosis of myxoid chondrosarcoma. Radical excision of a tumor was considered to play an important role in the management of intracranial myxoid chondrosarcoma.

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A 35-year-old man suffered secondary generalized tonic-clonic convulsions due to a large brain abscess. Neuroimaging incidentally revealed another tumor-like lesion. Cerebral angiography confirmed that the lesion was an unusual giant venous varix associated with a high-flow pial arteriovenous fistula (AVF) and showed one more small arteriovenous malformation (AVM). Pulmonary AVF, which can cause brain abscess, was also detected. Surgical ligation of the AVF and removal of the small AVM via individual craniotomies resulted in successful extirpation of the cerebrovascular malformations. Although the typical mucocutaneous symptoms were absent in this patient, the combination of arteriovenous anomalies was highly suggestive of hereditary hemorrhagic telangiectasia.

BACKGROUNDBow hunter’s syndrome or stroke (BHS) is characterized by rotational vertebrobasilar insufficiency elicited by rotation of the neck. It is caused by dynamic and reversible occlusion of the vertebral artery (VA). Reversible symptoms of rotational vertebrobasilar insufficiency are described as bow hunter’s syndrome, although brain infarction is rarely reported as bow hunter’s stroke.OBSERVATIONSA 70-year-old man experienced repeated cerebellar infarctions three times in the posterior inferior cerebellar artery (PICA) distribution of the nondominant right VA connecting the basilar artery. The onset of symptoms indicating cerebellar infarcts and the patient’s head position changes were unrelated. Dynamic digital angiography (DA) revealed that the nondominant right VA was occluded by an osteophyte from the C4 vertebral body, and the right PICA branches were shown to be passing through the distal right VA from the left VA. These findings were observed when the patient’s head was tilted to the right. An arterio-arterial embolic mechanism was suggested as the cause of repeated cerebellar infarctions.LESSONSTransient nondominant VA occlusion has been rarely reported as a cause of BHS when the head is tilted. To confirm the diagnosis of BHS, additional head tilt is recommended when performing dynamic DA in patients with a cervical osteophyte.