Complex intracranial venous circulatory disorder in achondroplasia

Clinical history
A 1-year-old boy was admitted for head enlargement and psychomotor delay. He was born at term with a head circumference of 35 cm, and the diagnosis of achondroplasia was made by specific clinical and radiographic findings. His head circumference rapidly increased during the first three months of life and then followed the curve of 1 standard deviation above the mean head circumference established for males with achondroplasia.
At clinical examination, the head circumference was 52.5 cm, the anterior fontanel was tense and the scalp veins were distended. Language was limited to babbling sounds. Examination of the cranial nerves was normal. In the sitting position, which was not possible without support, the head was not fully controlled. Spontaneous limb motion was poor but no pyramidal signs were found. The optic fundi were normal. Median nerve stimulation did not induce evoked somatosensory potentials at a supracervical level.

(exam 1) Achondroplasia 0.5 T
Complex intracranial venous circulatory disorder in achondroplasia
Fig.1 Lateral plain X-ray film of the skull. Macrocrania and characteristic disproportionate development of the cranial base compared to the cranial vault.
Fig. 2 Transverse CT image using high resolution algorithm and bone windowing. The jugular foramina appear narrowed on both sides (arrows).
Fig. 3 The foramen magnum diameter and cross sectional surface are 16 mm and 208 square millimeters respectively. The former is in the lower range of values reported in achondroplastic children [6].
Fig.4 3D reconstruction simulating a view of the foramen magnum from above provide a complementary approach to the evaluation of the morphology of the skull base and the narrow foramen magnum.
Fig.5 Sagittal T1-weighted spin echo image. Compression of the spinal cord is seen at the cranio-cervical junction. Other characteristic morphological abnormalities, such as rostral displacement of the brainstem with concomitant decrease of the optic tract angle (determined by the intersection of a line extending along the plane of the cribriform plate and the optic tract extending superiorly) can be observed [15].
Fig.6 Transverse proton density and T2-weighted fast spin echo images. Moderate enlargement of the ventricles is noted as well as the pericerebral subarachnoid spaces. Note the abnormal morphology (suggesting abnormal function) of the left superior ophthalmic vein (arrow).
Fig.7 A dilated, tortuous superior ophthalmic vein is identified in the upper part of the left orbit on magnified transverse proton density and T2-weighted images.
Fig.8 Global overview of the venous structures of the skull base on an transverse MIP reconstruction of a 2D TOF sequence, demonstrating the stenosis of both internal jugular veins at the level of the jugular formina (arrows).
Fig. 9 Sagittal targeted MIPs from the same 2D TOF acquisition provide clear evidence of hemodynamically significant stenoses (arrows) of both internal jugular veins at the level of the jugular foramina.
Fig. 10 Transverse targeted MIP from the same 2D TOF acquisition. The jugular stenosis is more marked on the right side (arrow).
Fig. 11 A rapid survey 2D Phase Contrast acquisition (36 seconds) shows flow in the dilated right superior ophthalmic vein.
Fig. 12 A sagittal targeted MIP reconstruction from a 3D Phase Contrast acquisition allows more detailed analysis. Direct connection between the right transverse sinus and the ipsilateral superior ophthalmic vein is seen, through the superior petrosal and the cavernous sinuses. Note also the unusually developed orbital absidal veins.
Fig.13 Transverse targeted MIP reconstruction from the same 3D Phase Contrast acquisition data set. Same observations as on Fig.12. These images provides evidence of the possibility of venous bypass towards the facial and external jugular veins from the morphological point of view (due to functional hypertrophy of the pre-existing venous pathways) secondary to internal jugular vein stenosis or occlusion.

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