Spinal muscular atrophy type I: Werdnig-Hoffmann disease

Findings

Figure 1, Figure 2, Figure 3: There is diffuse cerebral edema with loss of grey-white interface. A "hyperdense" cerebellum and hyperdense MCA vessels are seen. These are, in fact, normal in attenuation, but appear bright when compared with the hypoattenuated adjacent edematous brain.
Figure 4, Figure 5, and Figure 6: MR images demonstrate periventricular cystic spaces and are evidence of remote ischemic changes. There is a subdural fluid collection.


Diagnosis: Spinal muscular atrophy type I: Werdnig-Hoffmann disease


Spinal muscular atrophy (SMA) collectively refers to a family of disorders characterized by progressive degeneration of motor neurons in the spinal cord and brainstem. These disorders are inherited in an autosomal recessive pattern, with deletions or mutations in the survival motor neuron (SMN) gene at the 5q11 locus. Patients present with diffuse symmetric proximal muscle weakness, which is more pronounced in the lower extremities.

In general, there are three recognized types of SMA. These three types are clinically distinguished from one another based upon the age at presentation and the severity of disability. An earlier onset of disease correlates with a worse prognosis, however prognosis is primarily attributed to the severity of muscle weakness.


SMA Type: 1 = Werdnig-Hoffmann Disease

Age at presentation: Preterm – 6 mo
Clinical presentation: Hypotonia, unable to sit without support
Prognosis: Few survive 1 year; death by age 2


SMA Type: 2 = Intermediate type

Age at presentation: 6 mo – 15 mo
Clinical presentation: Proximal weakness; able to sit; unable to stand or walk unaided
Prognosis: Death due to respiratory complications, usually > 2 yo


SMA Type: 3 = Kugelberg-Welander Disease

Age at presentation: 12 mo – adolescence
Clinical presentation: Delayed motor development; able to stand and walk
Prognosis: Death in adulthood


Werdnig-Hoffman disease is both the most severe and the most common form of SMA. Mothers may report decreased fetal movement during the last trimester of pregnancy, and neonates typically present with generalized hypotonia. Involvement of the bulbar muscles leads to difficulty feeding, aspiration, and pneumonia. Involvement of the diaphragm and intercostal muscles leads to progressive respiratory insufficiency. All of these factors result in chronic hypoxia, and eventually death.

The diagnosis of SMA in patients presenting with the appropriate clinical signs and symptoms is confirmed with electromyography, nerve conduction studies, muscle biopsy, and molecular (genetic) analysis. Treatment is primarily supportive.

Hypoxic-ischemic injury to the brain in the term infant is dependent on two factors: the length of the hypoxic episode and the degree of the hypoxia. The damage caused as a result of partial hypoxia differs from that of profound asphyxia.

Chronic respiratory insufficiency in the term neonate will cause neuronal cell death, leading to generalized cerebral cortical atrophy and edema. Central structures (basal ganglia, thalami), and posterior fossa structures, are typically spared.

Total anoxia will lead to hypoxic-ischemic encephalopathy (HIE). In this case, the regions of the brain most affected are those with the highest metabolic demand. This includes the basal ganglia, thalami, hippocampi, brainstem, corticospinal tracts, and sensorimotor cortex.

In an infant with Werdnig-Hoffmann disease, CT scan will reveal:
- Decreased brain tissue attenuation
- Prominent sulci, intrahemispheric fissure, and dilated anterior subarachnoid space

MR is the most sensitive and specific imaging modality in the identification of neonatal hypoxic-ischemic injury. T2-weighted images of the spinal cord in Werdnig-Hoffmann disease will reveal high-signal intensity lesions in the region of the anterior horn secondary to motor neuron loss and associated edema.

Labyrinthine ossificans

Findings

Increased hazy densities bilaterally in the membranous component of the cochlea. The left tympanic membrane demonstrates focal thickening in the pars flaccidum. There is mild soft tissue density within the left external auditory canal. (Prior L left myringotomy tube).

Differential diagnosis:
- Labyrinthine ossificans
- Cochlear otosclerosis
- Cochlear aplasia
- Labyrinthine schwannoma
- Intravestibular lipoma


Diagnosis: Labyrinthine ossificans


Discussion

Labyrinthine Ossificans (LO) refers to ossification occurring within the luminal spaces of the labyrinth and cochlea. This typically is secondary to a destructive or inflammatory process and represents a healing response. Specific processes may be infectious, traumatic or surgical in nature. LO is most commonly seen after bacterial meningitis in children. Not surprisingly, LO secondary to bacterial meningitis represents the most common cause of acquired childhood deafness.

The typical clinical presentation is a child between 2-18 months of age with a history of recent meningitis presenting with bilateral sensorineural hearing loss. Although not a common presenting symptom, patients may also present with vertigo. Meningitis in the age group of interest is usually secondary to either streptococcus pneuomoniae or hemophilus influenzae.

Other presentations may include ear infection, bout of viral illness, or severe head trauma.

Ceftazidime is the antibiotic of choice to prevent otogenic and meningogenic labyrinthitis. This is secondary to the high antibiotic concentrations levels that can be reached in the CSF and endolymph. Steroids have shown some promise and are felt to decrease the rate of hearing loss. This is likely secondary to decreased inflammatory response, granulation tissue formation and collagen formation. Cochlear implantation may be an option if the cochlear nerve is still preserved. In cases of severe vertigo, labyrinthectomy may be warranted.


Radiologic overview

High resolution, 1 mm thick coronal and sagittal CT images are recommended. Post contrast images are not needed. The best clue on CT imaging is bone deposition within the membranous labyrinth. Findings vary based on the severity of the disease. Mild cases of LO may simply demonstrate increase haziness of the luminal spaces of the membranous labyrinth. Moderate cases may demonstrate areas of interspersed bone invading the luminal spaces. Severe cases may show complete destruction of the membranous labyrinth with extensive bony replacement of the luminal spaces.

Although CT imaging is used more often, MRI can be also assist in diagnosis. MRI offers the advantage of visualizing fibrous destruction of the membranous labyrinth which may be difficult to appreciate on CT. T2 weighted images are most useful in helping make the diagnosis. In mild LO, there is partial replacement of the hyperintense signal normally seen in the fluid spaces of the membranous labyrinth. In cases of moderate LO, hypointense focal areas are noted corresponding to bony replacement of the fluid spaces. Finally, complete absence of the T2 hyperintensity correlates with complete bony replacement of the fluid spaces seen in severe LO. As with CT, thin cuts on MR imaging are recommended.

Submandibular sialadenitis

Findings

There is diffuse soft tissue and glandular edema in the left sublingual and submandibular region. There is a large calcification in the left sublingual region representing a sialolith.

Differential diagnosis:
- Submandibular sialadenitis
- Submandibular carcinoma
- Malignant lymph node


Diagnosis: Submandibular sialadenitis


Key points

Presentation
- Unilateral painful submandibular gland (SMG) swelling with eating or salivation
- Painless mass

Treatment: Removal of submandibular gland in some cases.
Radiologic Evaluation: CT with contrast.

A sialolith is a calculus found in the salivary duct
- 85% are found in the submandibular duct, Wharton's duct
- 10% are found in the parotid duct
- 5% in the sublingual duct

Acute sialadenitis:
- Unilateral enhancing enlarged SMG with dilated duct behind the calculus
- Intraglandular ductal dilatation
- SMG cellulitis and/or myositis

Chronic sialadenitis:
- SMG small
- Fatty infiltration
- Intraductal calculus

Cystic hygroma (lymphangioma)

Findings

Fetal MRI reveals a large mass extending from the anterior palate to the right supraclavicular region. It involves the anterior right neck of the fetus, as well as the right masticator space, parapharyngeal space, carotid, and parotid spaces. The airway is not well visualized, presumably due to airway compression.


Diagnosis: Cystic hygroma (lymphangioma)


Key points

Incidence is 1:5000.
Caused by absent or abnormal connections between the lymphatic and venous systems, or from sequestration of embryonic lymphatic tissue.
50% association with chromosomal abnormalities.
Often missed in the first trimester, as the most common initial finding of increased nuchal lucency is difficult to detect.
In the second trimester, is most commonly identified on ultrasound as a cystic mass with multiple thin walled septations, frequently with a posterior midline band, representing the nuchal ligament.
Important to identify anterior cervical soft tissue involvement because of increased morbidity from respiratory compromise.
Important to differentiate from posterior encephalocele, which is associated with an underlying skull defect, and cervical myelomeningocele, which is associated with an underlying vertebral defect.
MRI is usually not necessary in diagnosis, although it is helpful for surgical planning. In this case, Cesarean section with head delivery was performed at 40 weeks gestation to maintain uteroplacental circulation while tracheostomy was created because of anterior neck involvement and airway compression. Bulk resection was performed 3 weeks later.

Silent sinus syndrome

Findings

Two coronal CT images (Figure 1 and Figure 2) and single axial CT image (Figure 3 ) demonstrate right maxillary sinus volume loss when compared to the left. There is inward retraction of the sinus walls (Figure 1, Figure 2, and Figure 3), increase in the size of the middle meatus (Figure 1 and Figure 2) and expansion of the retroantral fat (Figure 3). There is lateralization of the uncinate process and middle turbinate. This patient had concomitant right ethmoid air cell and frontal sinus opacification.


Diagnosis: Silent sinus syndrome


Silent sinus syndrome, or maxillary sinus atelectasis, is characterized by volume loss of the maxillary sinus after infundibular occlusion. It most often presents in the third through fifth decades of life with painless enophthalmos, facial asymmetry, and/or diplopia. Rarely do patients complain of symptoms of sinusitis.

Imaging findings of silent sinus syndrome are characteristic. There is maxillary sinus volume loss with inward retraction of the sinus walls and sinus opacification. The ethmoidal infundibulum is occluded, usually due to opposition of the uncinate process against the inferomedial orbit. The sinus volume loss accounts for the corresponding increase in ipsilateral orbital volume and size of the middle meatus.

The pathophysiology remains unclear. It is felt to be an acquired condition caused by chronic maxillary sinus obstruction and hypoventilation leading to negative intrasinus pressures. Chronic inflammation leads to osteolysis and thinning of the sinus walls which are retracted by the negative sinus pressure.

Treatment is aimed at creating an outlet for obstructed mucous via a nasal antral window or maxillary antrostomy. The goal of surgery is to prevent disease progression and further deformity.

Normal variant consistent with parietal foramina

Findings

On the ultrasound, there were 2 discrete bony defects in the skull, seen in the parietal regions bilaterally, that demonstrate sharp margins. These were each approximately 2 cm in diameter. The x-rays also demonstrate these same 2 round lesions.


Diagnosis: Normal variant consistent with parietal foramina


Key points

Parietal foramina are normal variants.
Normal parietal foramina transmit the emissary veins of Santorini (there can be a depression in the outer table at the vein's exit).
Defects are insignificant except in the differential diagnosis of bony defects (from surgical intervention or trauma).
These congenital defects have a characteristic location, but may vary in size.
These are often symmetric, although they can be asymmetric and irregular.

Oral cavity dermoid

Findings

Axial contrast enhanced CT (Figure 1 and Figure 2) demonstrate a well circumscribed cystic mass (Figure 1) in the root of tongue. The lesion is heterogeneous with focal oval areas of fat attenuation within the lesion. There is a thin wall with no significant surrounding inflammatory changes (Figure 3). The lesion is in the midline between the genioglossus muscles (Figure 4).


Diagnosis: Oral cavity dermoid and epidermoid


Epidermoid and dermoid cysts are benign lesions encountered throughout the body, with 7% occurring in the head and neck area. The orbit is the most common site in the head and neck for these congenital lesions. They rarely occur within the oral cavity, representing less than 0.01% of all oral cavity cysts.

These congenital cysts are dysembryogenetic lesions that arise from ectodermal elements entrapped during the midline fusion of the first and second branchial arches between the third and fourth weeks of intrauterine life. Acquired cysts may be derived from traumatic or iatrogenic inclusion of epithelial cells or from the occlusion of a sebaceous gland duct.

The cysts can be classified as epidermoid when the lining presents only epithelium, dermoid cysts when dermal appendages are found, and teratoid cysts when other tissue such as muscle, cartilage, and bone are present. The teratoid type is the only variety that may have a malignant change.

Anatomically, these oral cavity cystic lesions most commonly involve the floor of mouth and may occur in the root of tongue (ROT), submandibular space (SMS) or sublingual space (SLS). Dermoid cysts generally present with slow and progressive growth, and even if they are congenital, the diagnosis is usually possible in the second or third decade of life. Midline cysts of the floor of the mouth present as painless subcutaneous or submucosal lesions. When large, they can displace the tongue and result in dysphagia, dysphonia or dyspnea.

Epidermoids present on imaging as low density, unilocular, well circumscribed simple cystic lesion. Dermoid cysts are usually more heterogeneous with fatty internal material and possibly calcification.

The treatment of dermoid cysts of the floor of the mouth is extracapsular excision with an intraoral or external approach, depending on the size of the lesion and the position relative to the mylohyoid muscle. The entire cyst must be removed to prevent recurrence.