Chapter 3: Congenital anomalies or acquired disease? |
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Figure 3.10 Goldmann perimetry demonstrates near-complete bilateral inferior altitudinal defects.
showed questionable pallor superiorly. Possible mechanisms that were considered for this patient’s bilateral optic neuropathy included ischemia, compression, toxic injury and congenital anomaly.
Are there clues to the correct diagnosis in this case?
The diagnosis in this case can be deduced from two lines of evidence: the optic disc appearance and the family history. Careful inspection of the fundus reveals that the top of each optic disc is not actually pale but mal-developed (Figure 3.11). This disc appearance is diagnostic of a form of partial optic nerve hypoplasia that is found in the offspring of diabetic mothers. No additional testing was needed and the patient was reassured as to the benign and static nature of her congenital syndrome.
Discussion: Optic nerve hypoplasia is a congenital anomaly with a spectrum of clinical presentations. When severe and bilateral, the condition usually presents in infancy with poor fixation and nystag-
mus. The classic fundus picture is referred to as the “double-ring” or “halo” sign, in which a small optic disc is surrounded by a ring of bare sclera which usually is bordered by pigment (Figure 3.12). However, the appearance of optic disc hypoplasia is quite variable and the double-ring sign is found only in a minority of patients. In some cases, only a portion of the disc is hypoplastic, as in the above case, in which there is only half of a double-ring sign.
As in many congenital anomalies, the teratogenic insult is more time-specific than stimulusspecific. A variety of systemic events occurring at the six-week stage of embryogenesis have been associated with an increased risk of optic nerve hypoplasia (see Table 3.2). Optic nerve hypoplasia may occur as an isolated anomaly or may be associated with other abnormalities. The most common of these are absence of the septum pellucidum and agenesis of the corpus callosum, a constellation of findings termed septo-optic dysplasia, or De Morsier’s syndrome. Other less common abnormalities are cortical heterotopia, pachygyria and schizencephaly. Occasional cases
52 Chapter 3: Congenital anomalies or acquired disease?
Figure 3.11 Fundus photographs of the above patient with asymptomatic bilateral inferior altitudinal field defects. The upper margin of the true optic disc (arrowheads) is distinct from the edge of the scleral canal. This mismatch is diagnostic of superior segmental hypoplasia.
Figure 3.12 Fundus photographs of a child with optic nerve hypoplasia who presented in infancy with poor fixation and nystagmus. The discs are much smaller than the scleral canal (arrowheads indicate true disc margin in the right eye), leaving a variably pigmented gap and creating the classic “double-ring” sign. The right eye is affected more severely than the left.
Chapter 3: Congenital anomalies or acquired disease? |
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Table 3.2 Factors associated with an increased risk of |
ciated with other developmental anomalies. It is |
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optic nerve hypoplasia |
rarely present in patients who do not have a history |
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of maternal diabetes. The pathogenesis of superior |
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Young maternal age |
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segmental hypoplasia is unknown and it is particu- |
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First parity |
larly puzzling that such a focal deficit should result |
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Smoking |
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from a systemic metabolic abnormality. Individu- |
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Cytomegalovirus |
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als with this condition are asymptomatic since their |
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Toxins |
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visual world has been truncated since birth. Inferior |
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phenytoin |
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field loss is usually discovered during routine test- |
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lysergic acid diethylamide (LSD) |
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ing, as in our patient, or during the investigation of |
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phencyclidine (PCP) |
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an unrelated visual problem. |
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marijuana |
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alcohol |
Children with optic nerve hypoplasia should be |
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monitored for signs of developmental delay or |
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of optic nerve hypoplasia are associated with pan- |
growth failure. The risk of these complications is |
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greater in cases with severe bilateral visual loss and |
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hypopituitarism, even in the absence of other struc- |
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in such patients neuro-imaging and endocrinologic |
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tural brain abnormalities. If unrecognized, such |
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evaluation are usually undertaken at the time of |
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endocrine deficiency can lead to growth retarda- |
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diagnosis. In those with partial forms that are dis- |
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tion, developmental delay, diabetes insipidus and |
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covered in adult life, such as the patient presented |
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even sudden death. Panhypopituitarism may be |
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here with segmental optic nerve hypoplasia, no |
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predicted by the MRI which, on non-contrast T1- |
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ancillary testing is needed. |
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weighted images, typically shows that the normal |
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bright signal of the posterior pituitary gland is |
Diagnosis: Superior segmental hypoplasia |
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either absent or higher than normal, located in the |
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infundibulum. |
Tip: Superior segmental hypoplasia of the optic |
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Unilateral and segmental forms of hypoplasia are |
disc is a benign congenital anomaly that affects the |
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generally associated with good visual acuity. Growth |
offspring of diabetic mothers. A critical examination |
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delay and endocrine failure are uncommon in these |
of the fundus is diagnostic. |
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cases. A specific form of partial optic nerve hypopla- |
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sia that affects the offspring of insulin-dependent |
Incidental abduction deficit |
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diabetic mothers has been termed superior segmen- |
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tal hypoplasia or the “topless disc syndrome”. While |
Case: A 45-year-old homemaker had an eye exam- |
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initially considered to be a rare anomaly, a study of |
ination because of presbyopic symptoms. In the |
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34 offspring of diabetic mothers found a prevalence |
course of her evaluation it was noted that abduction |
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of 8.8%. This condition is usually bilateral, affects |
of the left eye was incomplete (Figure 3.13). She did |
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females more often than males, and is not asso- |
not experience diplopia but noted that images did |
Figure 3.13 Incomplete abduction of the left eye in an asymptomatic 45-year-old homemaker.