Imaging Studies
Neuroradiological abnormalities are reported in at least one third of the patients. Because many of the lesions are dysplastic or neuroblastic migration abnormalities, MRI is more useful than CT scanning.
Increase in the T2 signal of white matter is one of the most common findings. White matter abnormalities are somewhat predictive of a poor neurological outcome.
Neuroblast migration includes heterotopia, pachygyria, and polymicrogyria. Heterotopia may be observed at the level of the basal ganglia or as a periventricular band. Some of the dysplastic lesions may be localized, and hemimegalencephaly is also visualized.
Cerebral atrophy can be unilateral or generalized. Cases of cerebral hemiatrophy and porencephaly are often associated with a history of perinatal hypoxia or low birth weight.
Other rare imaging associations include the following:
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Noncommunicating hydrocephalus
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Megacisterna magna
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Arteriovenous malformation
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Cerebellar hypoplasia (hemispheres and vermis)
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Brainstem hypoplasia
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Brain tumors: MRI rarely reveals brain tumors; thus, patients occasionally have abnormal MRI findings but are neurologically healthy.
Brain imaging in patients with hypomelanosis of Ito (HI) and medically refractory epilepsy: The area that generates seizures (zone of ictal onset) should be found using a prolonged video-EEG, single-photon emission computed tomography (SPECT) or positron emission tomography (PET), and high-resolution MRI. If resective epilepsy surgery is a serious consideration after the preliminary tests are done (video-EEG, SPECT or PET) and the zone of ictal onset could not be determined, the patient may need to undergo invasive EEG monitoring with subdural grids or strips.
Other imaging tests
Musculoskeletal abnormalities often require radiography for proper quantification. A CT scan of the chest may be necessary when mediastinal tumors are investigated.
Abdominal ultrasonography may be required for diagnosis of genitourinary anomalies such as single kidney and urethral duplication.
Histologic Findings
Dihydroxyphenylalanine (DOPA) staining of the skin may reveal decreased size and number of melanosomes in hypopigmented areas. The melanocytes may be smaller and fewer, and their dendrites are short and sparse. Melanin incontinence (ie, melanin is absent in the epidermis but present in the deeper dermis) is not observed in patients with hypomelanosis of Ito. Histopathological alterations are not always typical; normal histology findings have been described in some cases. Neuropathological studies demonstrate polymicrogyria, disarray of cortical lamination, and heterotopic neurons in the white matter and giant cells.
Ultrastructural cutaneous studies may reveal normal-appearing basal and malpighian keratinocytes but a lack of melanosomes in the malpighian cells. [11] Melanosomes are dramatically reduced in the basal keratinocytes and appear small, single, or clustered and surrounded by a membrane. Melanocytic degeneration may be evident, and dendritic melanocytes contain various stages of nonmelanized premelanosome (stage II), partially melanized premelanosome (stage III), and, rarely, stage IV melanosomes. Unmyelinated axons of nerve-containing melanosomes may be seen at the dermoepidermal junction. Abnormal nerve termination has been observed in close relationship with basal keratinocytes, degenerated melanocytes, premelanosomes, and Langerhans cells.
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Hypomelanosis of Ito on the torso.
