Glomus tympanicum

Findings

There is a 2 mm mass arising from the right cochlear promontory without bony erosion.

Differential diagnosis of a vascular middle ear mass:
- Glomus tympanicum
- Congenital cholesteatoma
- Aberrant internal carotid artery
- Dehiscent jugular bulb
- Hemangioma


Diagnosis: Glomus tympanicum


Key points

Glomus tympanicum is a benign hypervascular tumor that arises from glomus bodies (neural crest tissue).
Glomus bodies in the middle ear are situated along Jacobson's nerve (a branch of CN IX) which forms the tympanic plexus. Branches of the tympanic plexus (and potential locations for glomus tympanicum tumors) occur on the cochlear promontory, near the round window, eustachian tube egress, tensor tympani tendon and along the inferior tympanic canaliculus. The classic location is the cochlear promontory.
On CT, the tumors are typically small, do not erode the bone (as opposed to cholesteatomas). On MR they demonstrate marked enhancement. Larger tumors may have a 'salt and pepper' appearance caused by flow voids in the mass.
Glomus tumors occur (in order of frequency) at the jugular foramen, branches of the vagus nerve (Arnold's nerve), carotid bulb or hypotympanum.
Overall glomus tumors are multiple in 15% of patients.

T1 hyperintense basal ganglia in a cirrhotic patient

Findings

Axial T1 weighted (SPGR) and sagittal FLAIR sequences demonstrate symmetric, increased signal in the basal ganglia, predominantly the globus pallidi bilaterally, (Figure 1 and Figure 3). However, abnormal increased signal extends from the midbrain (Figure 4), up to the head of the caudate (Figure 2). On T2 weighted images, the basal ganglia are unremarkable (Figure 5).

Differential Diagnosis:
- Deposition of Paramagnetic Substances:
Hemorrhage (methemoglobin)
Manganese (TPN, liver failure)
Copper (Wilson disease)
Melanin
- Calcification (ex-radiation/chemotherapy, hyperparathyroidism, Fahr disease)
- NF1, Halloverden-Spatz syndrome, Fucosidosis
- Japanese encephalitis
- Kernicterus
- Hypoxic-ischemic encephalopathy
- Chorea-Ballism associated with hyperglycemia


Diagnosis: T1 hyperintense basal ganglia in a cirrhotic patient


There are several causes of high T1 signal in the basal ganglia.

Obviously, clinical history or other imaging can be helpful in determining the underlying cause, as in this case. Additionally, the T2 characteristics and pattern of signal abnormality in terms of anatomic location and symmetry may suggest a particular etiology.

Hyperintense T1 signal in the basal ganglia, particularly the globus pallidus, has been observed in patients with chronic liver failure for some time. It has been postulated that paramagnetic substances, especially manganese, escapes hepatic clearance due to dysfunction and/or portosystemic shunting resulting in deposition in the basal ganglia. In a small autopsy series by Maeda et al, 3 patients with cirrhosis and T1 hyperintense basal ganglia all had significantly elevated manganese and copper in the globus pallidus and putamen. 1 patient with cirrhosis and no T1 hyperintense basal ganglia had normal levels of these substances. Individuals receiving TPN have identical findings on MRI, primarily from manganese deposition as well. When manganese is administered parenterally, it escapes the normal regulatory mechanisms, as in cirrhotics. In both patients on parenteral nutrition and those with liver failure, the signal abnormality may regress when TPN is stopped or hepatic function is restored

Characteristic MR findings in the basal ganglia in these patients include symmetric hyperintense signal on T1 weighted images, no signal change on T2 sequences, and no enhancement. CT attenuation in the basal ganglia is normal. The globus pallidus is predominantly involved however abnormal signal may extend from the tegmentum of the midbrain to the white matter. There is a direct relationship between the degree of signal abnormality and amount of deposition in the basal ganglia.

Ruptured dermoid tumor

Findings

CT head shows a 1.2 x 2.8 cm fat attenuation mass in the superior cerebellar cistern. Some smaller fat density foci are also seen in the midline of the cerebellum. MRI confirms a nonenhancing mass midline in the superior cerebellar cistern with T1-weighted hyperintensity (mass was approximately isointense on T2-weighted images and showed some FLAIR hyperintensity). Gradient imaging demonstrates a hypointensity similar in size to the hyperintensity on the T1 images.

Differential diagnosis:
- Ruptured dermoid
- Multiple lipomas
- Subarachnoid hemorrhage (MR images, depending on timing)


Diagnosis: Ruptured dermoid tumor


Key points

Dermoid lesions typically occur near the midline. Intracranially, they can be found parasellar, frontal, basal surface and in the posterior fossa most frequently in the superior cerebellar cistern and the fourth ventricle.
Dermoid tumors can rupture and release lipid contents into the ventricular or subarachnoid spaces. This may cause a chemical meningitis that can lead to recurrent symptoms, most commonly headache. Meningeal inflammation may result in arterial vasospasm and, rarely, stroke and death.
CT: Well-circumscribed, predominantly cystic mass with decreased attenuation in the range of -20 to -40 HU because of their fat content. May appear slightly heterogeneous due to additional ectodermal elements, including hair follicles, sebaceous glands, and sweat glands. Calcifications are frequent in the wall of the tumor.
MRI shows signal characteristics of fat. They are hyper intense on T1-weighted images and hypo intense on T2-weighted images.
Contrast enhancement is uncommon. If enhancement is present in a suprasellar tumor, other diagnoses should be considered including craniopharyngioma, teratoma, or germinoma.
Differential diagnosis for substances that are hyper intense on non-enhanced T1-weighted images include fat, proteinaceous material, methemoglobin, manganese, calcium, liquid cholesterol, melanin, and Pantopaque contrast.
Fat-suppression techniques may be helpful to confirm the presence of fat in the lesion and chemical shift artifact is frequently seen.
Centrally, dermoid tumors may appear inhomogeneous due to the presence of hair follicles, calcifications, and cellular debris.
Fat droplets in the ventricular or subarachnoid spaces strongly suggest rupture of a dermoid tumor.

Gorlin-Goltz syndrome

Findings

Extensive dural calcifications on head CT (that patient had also poor dentition with evidence of multiple dental caries with a cystic lesion in the left mandible, which demonstrates a narrow zone of transition and benign appearing characteristics and a mass in superficial soft-tissues of hand overlying 5th MCP joint.


Diagnosis: Gorlin-Goltz syndrome


Discussion

When multiple odontogenic keratocysts are present in a young person, the diagnosis of basal cell nevus syndrome (also known as Gorlin-Goltz Syndrome) should be considered. Approximately 5% of patients with odontogenic cysts have this syndrome. Associated findings of basal cell nevus syndrome include calcification of the falx cerebri, midface hypoplasia, frontal bossing, mental retardation, bifid ribs, and multiple basal cell carcinomas. Basal cell nevus syndrome is an autosomal dominant disease with high penetration. Early identification of these patients is important for improving their quality of life and survival.


Radiologic overview of the diagnosis

Key radiographic findings in basal cell nevus syndrome include odontogenic keratocysts (as described above), rib anomalies, vertebral anomalies, dural calcifications, and short metacarpals. These patients are at increased risk for medulloblastoma and cardiac and ovarian fibromas.

Pathologic fracture of the left mandibular body through a compound odontoma and a fracture of the right mandibular ramus

Findings

Figure 1: The panorex demonstrates a displaced fracture of the right mandibular ramus near the angle, as well as a fracture line through the left parasymphseal mandibular body, through an incidental partially calcified mass.
Figure 2, Figure 3, and Figure 4: Axial, coronal, and sagittal CT images demonstrate a collection of radio-opaque tooth-like structures surrounded by a thin radiolucent peripheral rim. In addition, there are associated unerupted teeth.

Differential diagnosis for calcified masses in the mandible:
- Calcifying odontogenic cyst (Gorlin’s cyst)
- Calcifying epithelial odontogenic tumor (Pindborg tumor)
- Cementoma
- Fibrous dysplasia
- Foreign body
- Odontoma
- Ossifying fibroma
- Osteoma
- Synovial osteochondromatosis
- Focal sclerosing osteomyelitis
- Chondrosarcoma
- Osteosarcoma
- Metastasis


Diagnosis: Pathologic fracture of the left mandibular body through a compound odontoma and a fracture of the right mandibular ramus


Embyrologically, the dental lamina proliferates along the future dental arches. At intervals beneath the lamina, tooth buds are formed, each composed of an enamel organ, a dental papilla, and a dental sac.

The enamel organ differentiates to include ameloblasts, which elaborate enamel in response to the production of dentin by odontoblasts within the underlying dental papilla. The dental sac forms both a layer of cementum around the dentin that covers the root, as well as the periodontal ligament, which attaches the cementum to the surrounding bone.

Odontogenic cysts and tumors are derived from the enamel of the tooth crown, epithelial remnants from the root sheath or dental lamina, or from the tooth germ itself (the enamel organ, dental papilla, and dental sac). Symptoms, when present, may be related to tooth devitalization, secondary infection, absence of teeth due to impaction or lack of development of the normal tooth, convergence of crowns due to a mass growing between the roots of two teeth, or expansion of the mandible or maxilla itself.

Generally asymptomatic except for their association with unerupted teeth, odontomas are the most common type of odontogenic tumors. They represent a hamartomatous growth of ameloblasts and odontoblasts, which abnormally elaborate enamel and dentin within the mass. Compound odontomas are generally located in the anterior jaw and by definition contain denticles, structures within the mass with the macro- and microscopic appearance of small teeth. In contrast, complex odontomas are generally found in the molar regions of the jaw and contain disorganized dental tissue. Complex odontomas require histopathologic analysis to differentiate them from other lesions.

Odontomas generally undergo surgical enucleation due to malpositioning and impaction of adjacent teeth. In addition, the epithelial components can give rise to a dentigerous cyst. The lesion does not recur after excision.

Glutaric aciduria type I

Findings

There is diffuse cerebral volume loss (atrophy) with dilated bilateral Sylvian fissures and old bilateral putamenal infarcts. In addition, there is increased T2 signal intensity throughout the subcortical white matter without restricted diffusion.

Differential diagnosis:
- Remote trauma or non-accidental trauma
- Glutaric aciduria type I
- Bilateral middle cranial fossa arachnoid cysts
- Mucopolysaccharidoses (types I-VII, Hurler)
- Canavan disease


Diagnosis: Glutaric aciduria type I


Key points

Glutaric aciduria type I (GA1) is an inborn error of metabolism - a mitochondrial disorder resulting in glutaryl-coenzyme A dehydrogenase (GCDH) deficiency. CGDH is involved in the metabolism of lysine and tryptophan.
Patients suffer from encephalopathic crises and experience severe dystonic-dyskinetic movements.
Patients initially develop normally. Most will become severely disabled. 20% die before age 5.
Early treatment can prevent or lessen symptoms.
Common imaging features include widened operculae (frontotemporal atrophy) – so called "bat wing" configuration of the Sylvian fissures. Also common are bright basal galglia and diffuse white matter gliosis.
Can mimic child abuse. Marked cerebral atrophy predisposes these children to bridging vein injuries resulting in subdural hematomas from minor trauma.

Acquired cholesteatoma (Pars tensa type)

Findings

Figure 1: The axial CT image demonstrates the presence of a soft tissue mass in the middle ear with an intact jugular fossa.
Figure 2: The coronal CT image demonstrates a soft tissue mass and severe erosive change involving the epitympanic ossicular chain. There is lateral displacement of the residual epitympanic ossicular mass with an intact scutum.


Diagnosis: Acquired cholesteatoma (Pars tensa type)


Acquired cholesteatomas arise from a perforation of the tympanic membrane. The perforation may be secondary to otitis media, trauma, or surgical manipulation and allows stratified squamous epithelium to grow into the middle ear cavity. Essentially, acquired cholesteatomas represent erosive collections of keratinous debris. The critical imaging feature in identifying a middle ear soft tissue mass as a cholesteatoma is the presence of bony erosion.

The pars tensa variety of acquired cholesteatoma is much less common than pars flaccida cholesteatomas. The pars tensa is the tougher posteroinferior portion of the tympanic membrane and is not as prone to rupture as the weaker anterosuperior pars flaccida. Pars tensa cholesteatomas present with a mass in the middle ear, erosion of the long process of the incus or stapes, ossicular displacement, and epitympanic spread. The scutum is usually intact. Pars tensa cholesteatomas are also known as “sinus” cholesteatomas because of their tendency to spread to the sinus tympani and other recesses of the posterior tympanum. Spread from the posterior tympanum is typically superomedial or superolateral toward the additus.

The majority of acquired cholesteatomas involve the pars flaccida and Prussak’s space. Virtually all of the boundaries of Prussak’s space can be identified on CT. The lateral border consists of the pars flaccida and the inferolateral wall of the epitympanum (attic), while the medial border consists of the head of the malleus and the body of the incus. The short process of the incus defines the inferior border. Only the lateral mallear ligament, which forms the superior and anterior borders of Prussak’s space, cannot always be readily identified on CT. The head of the malleus and body of the incus are most susceptible to erosion by pars flaccida cholesteatoma. Erosion of the scutum is also frequently present. Lysis of the entire ossicular chain is uncommon.

The hallmark symptom of a cholesteatoma is painless otorrhea. Hearing loss from ossicular chain damage is another common symptom. Dizziness is relatively uncommon but may occur if the cholesteatoma is lying directly on the footplate of the stapes. A complication of cholesteatoma that may also result in dizziness is the development of a labyrinthine fistula from bony erosion. Other complications include erosion of the tegmen tympani (the roof of the epitympanic space) and subsequent invasion of the intracranial compartment. The lateral or inferior wall of the facial nerve’s tympanic portion is another area of potential erosion.

Computed tomography is the imaging modality of choice for the diagnosis of cholesteatoma. MRI may be utilized to evaluate for very specific problems such as dural involvement, subdural or epidural abscess, inflammation of the membranous labyrinth, and sigmoid sinus thrombosis. Cholesteatomas are hypointense on T1WI and intermediate signal intensity on T2WI. One important difference between cholesteatomas and granulation tissue is that cholesteatomas do not enhance.

The standard of care for treatment of cholesteatomas is surgical excision. Even though multiple operations may be required, removal of a cholesteatoma is almost always possible. Surgery is generally successful and complications from uncontrolled cholesteatoma growth are now relatively uncommon.