INTRAOSSEOUS-HETEROTOPIC GANGLIONS OF THE TIBIA

DISCUSSION

Although well recognized as an entity, there has been a lot of confusion amongst fellow orthopaedic surgeons regarding the appropriate term for an intra-osseous ganglions. Despite having a close relationship to the neighbouring joints they seldom have been found communicating with them as reported by Carp and Stout (1928) in their experience with 225 ganglia.[2]

They bear an identical resemblance to the frequently found ganglia, commonly seen or the dorsum of the wrist, but controversy rages regarding its actual Pathogenesis with many theories proposed but non proven conclusively.

1. Theory of synovial herniation[3] was proposed seeing its proximity to the nearby joint, arising from the joint capsule or tendon sheath due to a defect or a traumatic tear.[3] However, rarely has any communication between the lesion and joint clearly demonstrated. According to Nigrisoli and Beltrami, the intraosseous cysts are subjected to trauma and in 2 of their 4 cases found a crack extending between the lesion and the adjacent articular surface, which was due to a pumping action of joint fluid in the subchondral spongisa.[4]

2. Theory of benign neoplasia - is made plausible by post surgical recurrences but is not entirely explainable in view of cures reported by simple rupture, with sclerosing agents which solely affect the surface linings.[5]

3. Theory of synovial rests - presumes that ganglia arise from synovial remnants derived from developing periarticular tissues. However, embryological studies have shown no infolding of synovial membrane at any stage of joint formation from which such sequestra could be produced.[6]

4. Theory of metaplasia and/or connective tissue proliferation - This theory proposes that ganglia arise as a result of primary cellular hyperplasia associated with active cytoplasmic mucin secretion, whose accumulation within connective tissue stroma is responsible for the cystic stage. Subsequently fibroblasts were incriminated as a source of hyaluronic acid secretion.

5. Theory of mucoid degeneration - relates ganglia to connective tissue degeneration and subsequent liquefaction due to chronic damage. However, recent reports show active secretion of ‘mucin - like’ substance high in hyaluronic acid.

Although a number of these theories are proposed, none of them completely explain the origin of an intra-osseous ganglions, though histologically there is no difference between the former and soft tissue ganglions.

Though occasional cyst lining have been described as "synovial in type", in most cases intra-osseous ganglia lack a distinct cell type in their frequently incomplete lining, containing no synovial fluid and rarely any joint communication.[7] Lot of confusion has arisen in case of cysts seen around the hip joint, been confused as periarticular cysts of degenerative joint disease, a condition where articular cartilage disruption and joint communications frequently do exist. However, they are distinctly associated breaches in the compromised articular cartilage. Intra-osseous ganglions are very similar to the subchondral cyst of osteoarthritis and sometimes difficult to establish whether juxta-articular cyst is secondary to articular degeneration or the articular lesion are consequence of the cyst.[8] Trauma and inflammation too have been put forth as possible causes for intra-osseous ganglions. However, never has trauma been present prior to the complaints, nor have blood pigments found consistently. Also no evidence of any granulation tissue, abscess formation or inflammation cells been noted.[9]

A best possible theory would be a combination of intramedullary metaplasia and a proliferative process, followed by a degenerative process diagrammatically shown as[9]

	Intramedullary		Proliferation
Bone		Fibroblasts		Hyaluronic acid
	Metaplasia		Mucin secretion	Accumulation
					Pressure Atrophy
			Intramedully
			Trabecular
			Degeneration
			Intra-osseous cyst formation

Histology

Most of the intra-osseous ganglia lie sub-chondrally, though ours was in the diaphyseal region, with a normal articular cartilage and rarely connections demonstrated between them and joint spaces or tendon sheath overlying it. The intact cyst often appears relatively smooth, round to oval shaped, with an ochre-yellow colour similar to a soft tissue ganglia, containing a thick gelatinous material. Microscopically, the walls are composed of poorly vascularised fibrous tissue and the cavities incompletely lined by flattened connective tissue cells with, only occasionally, resemble synovial histocytes. Myxoid parts of these lesion result from interstitial mucopolysaccharides secretion. Chemical analysis has revealed a high concentration of hyaluronic acid and other mucopolysaccharides besides glucosamine, albumin and globulin.

Clinical Signs and Symptoms

These lesions present at various ages, with literature reporting a range from 14 years to 86 years with no preponderance for any particular sex.

The main complaint generally is a swelling with pain localized to the same and sometimes emanating from the near by joint due to osteoarthritis changes in the same. Many patients are also worried about the increasing size of the "tumour", thus seeking medical advice.

X-ray Findings

Many sites have been incriminated, of which the lower extremity was the commonest, with size ranging from 2 mm to 7 cm in diameter.

These lesions are lytic in character well demarcated and sharply circumscribed. At times one may encounter a pathological fracture, these lesions however rarely calcify.[10] A soft tissue shadow may be seen at times. Recently, an article described role of delayed radiography which showed evidence of communication between a sub-perosteal ganglions cyst and adjacent knee joint.[11] However this is not regularly done.

CT Scan - generally shows a hypodense image with respect to the surrounding muscles. Typically, contrast enhancement is absent although slight enhancement of the ganglions wall may be apparent.[12]

MRI appears similar to degenerative cysts, except that the overlying joint has a normal articulation. Intraosseous ganglions may or may not communicate with the joint. These lesions have a fluid like appearance with low intensity on T1 weighted MR images, moderately low intensity on proton density weighted images and high homogenous intensity on T2 images.[13]

Differential Diagnosis - This is generally a dilemma because of its rarity vis-a-vis other lesions. One has to keep in mind the age and site of the lesion to research to any conclusion and still a final answer may be available only after performing the surgery or the histopathology report. The differential diagnosis would include a wide range of conditions ranging from giant cell tumours, benign chondroblastoma, benign osteoblastomas, fibrous dysplasia, non-ossifying fibroma, etc. to just mention a few. One cannot but help mentioning "degenerative cysts" especially those close to the joints which can mimic an intra-osseous ganglions, particularly around the hip region.

However, with the advent of newer modalities of diagnostic aids like the MRI, one can, in most cases reach to the right conclusion in most cases, thus making the execution of treatment more predictable.

Treatment is invariably surgical, whether done for a symptomatic or an incidentally found one. Surgical excision of the lesion with bone grafting is advocated in large cavities and curettage in smaller lesions. There have been recurrences also reported, although they may not be due to inadequate excision or curettage, but could occur in conjunction with the connective tissue reparative process either at the operative site or in tissue immediately adjacent to it. The lesion may recur, even after an adequate excision by mucoid degeneration taking place in the periosteum immediately adjacent to the operative site or in the connective tissue occupying the surgical defect.[14]

SUMMARY

A brief review of intra-osseous ganglia has been attempted with special attention to its pathogenesis, clinical features and presentations taxing the most astute clinician.


Fig. 2: X-ray of the lesion - showing medical joint space narrowing with no evidence of any lyboic lesion.	Fig. 3: MRI - with ga scan showing enhancement suggestive of a infabric lesion.

Fig. 4: An in-sibu view of the lesion with co arising from rather the underlying tibia.	Fig. 5: A photograph of the complete lesion arised in to-to along with its underlying capsule.

Fig. 6: Histopathology of the lesion showing myxomatous mucuous tissues.