Orbital dermoid cyst

Dr Bruno Di Muzio et al.

Orbital dermoid cysts are congenital lesions representing closed sacs lined by an ectodermal epithelium and corresponding to the most common orbital tumour in children. They are typically divided according to whether or not they are deep (within the orbit) or superficial (adjacent to the orbital rim).

Epidemiology

They correspond to ~2% of orbital tumours 5. Superficial location is much more frequent.

Clinical presentation

Superficial angular dermoid are usually diagnosed relatively early. As they grow slowly, less than 25% of them are identified at birth, and they usually manifest in the first decade of life. Clinical features include painless subcutaneous mass along the zygomaticofrontal and the frontoethmoidal sutures 1,3.

It is important to note that more than 80% occur in the upper outer quadrant or the lacrimal fossa (external angular dermoid) 1.

Deep dermoids tend to be diagnosed later in life with proptosis 6.

Pathology

Dermoid cysts are thought to occur as a developmental anomaly in which embryonic ectoderm is trapped in the closing neural tube between the 5th-6th weeks of gestation1,3.

Stratified squamous epithelium lines dermoid cysts, like epidermoid cysts. Unlike epidermoid cysts, however, they also have epidermal appendages such as hair follicles, sweat and sebaceous glands. The latter is responsible for the secretion of sebum which imparts the characteristic appearance of these lesions on CT and MRI.

A common misconception is that dermoid cysts contain adipose tissue. This is not the case, as lipocytes are mesodermal in origin, and dermoid cysts (by definition) are purely ectodermal. A dermoid cyst with adipose tissue would be a teratoma.

Radiographic features

These lesions are usually extraconal, non-enhancing masses with smooth margins, cystic and/or solid components which are demonstrated on imaging by fat, fluid or soft tissue signal; occasionally calcifications may be present. Ruptured dermoids may show adjacent inflammatory changes (see case 2).

Treatment and prognosis

Treatment and prognosis depend on size, location and involvement of orbital structures. While a superficial lesion may barely need a cosmetic excision, a deeper one may require more invasive methods involving micro-dissection, orbitotomy, and rarely intracranial exploration if the lesion extends to that extent 7.

Differential diagnosis

Possible differential considerations include

• orbital epidermoid cyst
• orbital teratoma
  • usually large lesions and associated with facial deformity
  • multiloculated cystic masses
  • calcification, fat, and/or ossification may be present
• orbital dermolipoma
• orbital haemangioma

Cases and Figures

Loose right total hip prosthesis

Case contributed by Jack Ren

Presentation

Loose right femoral component.

Patient Data

Age: 70

Gender: Female

Bilateral cemented total hip prosthesis. Ideally comparison would be made with previous films but note the steepness of the right acetabular cup compared to the more normal angle of approximately 500 to horizontal on the left. This may be due to poor positioning at the initial surgery or because the cup has rotated.

Lucent regions are seen between the cement and bone along the mid and distal femoral stem. There is also lucency between the shoulder of the right femoral stem and the greater trochanter indicating subsidence. Findings are those of loosening of both the right acetabular and femoral components. The left hip replacement is normal.

Pitt pit

A.Prof Frank Gaillard◉ et al.

Pitt pit refers to an oval or round lucency in the anterosuperior aspect of the femoral neck, just distal to the articular surface. It represents a herniation of synovium or soft tissues into the bone through a cortical defect, hence the alternate name synovial herniation pit. They are usually around 5 mm in diameter but can be anywhere between 3 mm and 15 mm.

They are most often an incidental finding and of no clinical significance. There is debate about the exact aetiology of herniation pits. There is some evidence that they may result from femoroacetabular impingement as around 30% of patients with this condition are found to have such a pit2.  

Pitt pit is one of the skeletal “don’t touch” lesions.

Cases and Figures

Case 1

Case 2: two pits

Case 3

Case 4

Case 5

Case 6

Gout

Case contributed by Dr Tim Wastney

Presentation

85-year-old male. Hand and foot pain.

Patient Data

Age: 85 years

Gender: Male

Modality: X-ray

X-ray

Frontal

The DIP joint of the right index finger is affected by juxta articular erosion. The distal erosion has an overhanging margin. Some erosive change seen on the radial side of the IP joint of the right thumb. Also mild changes in the distal interphalangeal joints of the left index and middle fingers. Periarticular osteopenia is seen surrounding the MCP joints and IP joints of both hands.

Modality: X-ray

• 
  Frontal
• 
  Frontal

X-ray

Frontal

Juxta-articular erosions with overhanging margins involving the metatarsophalangeal joint of both big toes, with associated soft tissue swelling and relative sparing of the joint space. Similar changes involving the distal interphalangeal joint of the left fourth toe

Case Discussion

Imaging appearances are fairly characteristic of gouty arthritis involving multiple joints in an asymmetric fashion.