Silent Sinus Syndrome

Silent sinus syndrome (SSS), also known as Maxillary atelectasis with enophthalmos and imploding antrum, is the painless (silent) involution of the maxillary sinus with associated enophthalmos due to gradual collapse of the orbital floor.

It is thought that SSS is caused by hypoventilation of the maxillary sinus due to obstruction of the ostiomeatal complex. The trapped gas is resorbed into capillaries, creating negative pressure. There is also accumulation of secretions and chronic inflammation, resulting in maxillary atelectasis and wall collapse.

Patients present with enophthalmos (2-5 mm). Diplopia and other ocular symptoms are uncommon, likely due to the gradual course of the disease.

CT findings include:

• Complete or near-complete unilateral obstruction of the maxillary sinus
• Obstruction of the ostiomeatal unit
• Lateral retraction of the uncinate process, resulting in relative enlargement of the middle meatus
• Nasal septal deviation
• A variable degree of retraction and collapse of all the walls of the maxillary sinus, manifested as concavity, resulting in inferior displacement of the globe and orbital contents into the maxillary sinus
• Demineralization of sinus walls
• Increased retroantral fat pad on the affected side

References

• Annino DJ Jr, Goguen LA. Silent sinus syndrome. Curr Opin Otolaryngol Head Neck Surg. 2008 Feb;16(1):22-5.
• Waqar S, Dhir L, Irvine F. Silent sinus syndrome: a cause of unexplained enophthalmos. Can J Ophthalmol. 2010 Oct 24;45(5):547-548.

Bizarre Parosteal Osteochondromatous Proliferation

25-year-old man with 2 years of progressively worsening pain at the small finger with recent loss of range of motion.  

Bizarre parosteal osteochondromatous proliferation (BPOP), also known as Nora lesion, is an osteochondromatous proliferation that arises from the periosteal aspect of an intact cortex. The lesion occurs most commonly in the hands and feet (proximal and middle phalanges, and metacarpals/metatarsals) of young adults. About 25% of cases occur in the long bones.

It is thought to be part of a spectrum of reactive changes in response to trauma, initially presenting as soft-tissue swelling.

The stage after soft-tissue swelling is florid reactive periostitis, where there is a laminated or mature periosteal reaction and often minimal periosteal elevation. There is juxtacortical soft tissue calcification, without disruption of the underlying cortex or medullary changes.

The next stage is BPOP, where there is a well-marginated mass of heterotopic mineralization arising from an intact cortex without periosteal reaction or medullary changes.

The final stage is acquired osteochondroma or turret exostosis, where the focus of ossification matures and a bony base is formed with a cartilage cap.

Histologically, BPOP is composed of variable amounts of cartilage (usually predominant), bone, and fibroblastic spindle cells and is similar to fracture callus. The cartilagenous component can have areas of ossification, and large immature chondrocytes can raise concern for malignancy. The rest of the lesion consists of trabeculae of woven bone mixed with fibroblastic spindle cells.

Differential Considerations

• Osteochondroma: There is continuity of the intramedullary cavity with the lesion in osteochondroma. BPOP, as described above, is not continuous with the medullary cavity. In addition, there is absence of the characteristic orientation away from the physis in BPOP.
• Myositis ossificans: There is ossification along the periphery of the lesion, which is located in the peripheral soft tissues.
• Parosteal osteosarcoma: There is cortical and soft-tissue infiltration and periosteal elevation, which are not seen in BPOP.

References

• Bush JB, Reith JD, Meyer MS. Bizarre parosteal osteochondromatous proliferation of the proximal humerus: case report. Skeletal Radiol. 2007 Jun;36(6):535-40.
• Dhondt E, et al. Nora's lesion, a distinct radiological entity? Skeletal Radiol. 2006 Jul;35(7):497-502.
• Hoch B, Montag A. Reactive bone lesions mimicking neoplasms. Semin Diagn Pathol. 2011 Feb;28(1):102-12.

Multiple Meningiomas

Meningiomas are multiple in up to 10% of imaged cases and up to 17% in autopsy series. However, the presence of multiple meningiomas in different neuraxial compartments is rare. In about 30% of cases, different histological types of meningioma are seen in the different lesions.

Cushing and Eisenhardt used the term "multiple meningiomas" to refer to the occurrence of multiple meningiomas in the absence of neurofibromatosis or vestibular schwannomas.

References

• Cushing H, Eisenhardt L. Meningiomas; their Classification, Regional Behaviour, Life History, and Surgical End Results. Springfield III., Charles C Thomas, 1938, 785.
• Bhatoe HS. Simultaneous occurrence of multiple meningiomas in different neuraxial compartments. Neurol India. 2003 Jun;51(2):263-5.

Scheuermann Disease

Scheurmann disease refers to vertebral wedging, end-plate irregularity, and disc height loss, with or without Schmorl nodes, classically resulting in thoracic (75%) kyphosis. The thoracolumbar (25%) and lumbar (5%) spine may also be involved. Cervical spine involvement is rare. It is seen in adolescents and young adults, found in 30% of boys and 20% of girls with back pain. 15% of patients also have scoliosis.

The criteria for the diagnosis of Scheuermann disease are:

• Greater than 5-degree wedging of at least three adjacent vertebrae at the apex of the kyphosis
• Irregular and narrowed endplates
• Thoracic kyphosis of greater than 45 degrees

References

Davies A, Saifuddin A. Imaging of painful scoliosis. Skeletal Radiol. 2009 Mar;38(3):207-23.

Differential Diagnosis of Painful Scoliosis in a Child

Scoliosis in adults often presents with pain. Idiopathic scoliosis in children, on the other hand, is often painless. When children present with painful scoliosis, especially if there is a left-sided curve, the following conditions should be considered:

• Vertebral tumours: osteoid osteoma, osteoblastoma, aneurysmal bone cyst, Langerhans cell histiocytosis
• Intraspinal tumours: neurofibroma; astrocytoma
• Infection: tuberculosis, discitis, osteomyelitis
• Scheuermann kyphosis
• Disc disease: disc herniation, Schmorl nodes
• Spondylolysis: spondylolisthesis
• Degenerative: facet joint arthritis, spinal stenosis, nerve root compression

References

• Taylor LJ, Painful scoliosis: a need for further investigation. Br Med J (Clin Res Ed). 1986 January 11; 292(6513): 120–122.
• Davies A, Saifuddin A. Imaging of painful scoliosis. Skeletal Radiol. 2009 Mar;38(3):207-23.

Double "Density" Sign on Bone Scan

The double "density" sign, more properly referred to as the double uptake sign, is the scintigraphic pattern on osteoid osteoma on bone scan. The more intense central uptake on blood-flow, blood-pool and delayed phases of the bone scan represents the nidus of the lesion, while the lower, peripheral uptake, represents activity in the surrounding sclerotic reactive bone. The main differential considerations on radiographs include osteomyelitis, which has a more uniform pattern of radiotracer uptake, and abscess, which has decreased activity in the central cavity.

Epiphyseal Lesions: Differential Diagnosis

• Giant cell tumor:
• Chondroblastoma:
• Langerhans cell histiocytosis:
  
  
• Subchondral cyst:
• Infection: Pediatric osteomyelitis
• Lymphoma:
• Metastasis:
• Osteoid osteoma: Rarely involves the epiphysis
• Clear cell chondrosarcoma: Rare