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An unusual presentation of calvarial tuberculosis

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Q1: What is the differential diagnosis and what other investigations are indicated?

The differential diagnosis of multiple osteolytic lesions of the skull would include metastases, multiple myeloma, histiocytosis and pyogenic, fungal, or tuberculous osteomyelitis.

Investigations for this case should include the work-up for primary malignancy, myeloma, tuberculosis, or other systemic infections and chronic inflammatory disease. Apart from a raised erythrocyte sedimentation rate (75 mm at one hour), routine haematology was normal. Chest radiography showed mildly prominent hilar opacities. Ultrasound of the abdomen revealed mild enlargement of the para-aortic lymph nodes. The bone scan showed hot spots in the corresponding regions in the skull and also in D4, D12, and L4 vertebrae. Urinary Bence-Jones proteins were negative.

Since the laboratory and radiological investigations were inconclusive, the patient underwent an open biopsy of the right frontal bone lesion for a definitive diagnosis. At surgery the scalp was normal. Soft granulation tissue was encountered where the cortical bone was destroyed. There was no extradural granulation tissue. The histopathological examination was consistent with tuberculosis showing non-caseating granulomata composed of epitheloid histiocytes and multinucleated giant cells of Langhan's and foreign body type.

Q2: What are the different forms of calvarial tuberculosis and what is the common presentation?

The different radiological forms of calvarial tuberculosis described are1:

  • Circumscribed lesions of the sclerotic and lytic type.

  • Diffuse tuberculosis of the cranium.

Though the bony involvement maybe variable calvarial tuberculosis often presents with painful scalp swellings, subgaleal collections, discharging sinuses, and variable amount of extradural granulation tissue. Isolated skull bone involvement is rare.

Q3: What is the management of this condition and indication for surgery?

Management of calvarial tuberculosis includes establishment of the diagnosis and adequate antituberculous therapy, along with appropriate surgical intervention. An urgent surgical intervention is indicated in the presence of large extradural collections causing mass effect and neurological deficits. The presence of large collections of pus in the subgaleal plane and sinus formation necessitates thorough debridement and excision of the sequestrum along with the infected granulation tissue. Associated secondary infection needs treatment with appropriate antibiotics. Finally an excision biopsy of the lesion would be indicated, to establish the diagnosis, where there is high index of suspicion and other results are inconclusive. Surgical treatment should always be followed by adequate antituberculous therapy, considering the indolent nature of infection.

Learning point

Tuberculous osteomyelitis should be considered in the differential diagnoses of multiple lytic lesions of the skull especially in endemic areas. High index of suspicion and excision biopsy can lead to early diagnosis and good outcome.

Discussion

Calvarial tuberculosis was first reported by Reid in 1842.1 It usually occurs secondary to haematogenous spread from a primary focus elsewhere in the body that may not always be evident. Trauma and surgery can result in direct inoculation of the organism.2,3 It is also proposed that the increased vascularity and transient decreased resistance at surgery may result in specific homing of bacilli, as the inflammatory cells are attracted to the site of trauma and act as vectors for the bacilli.1

Skull tuberculosis is very rare and is reported to occur in only 0.01% of patients with mycobacterial infections.4 Most cases occur in the first two decades; however infants are rarely affected, probably because of the paucity of cancellous bone in the skull.5 The frontal and the parietal bones are usually involved.6 The type of clinical presentation depends perhaps on the immunity of the individual.7 Once the marrow of the diploe is seeded with the inoculum, the infection spreads towards the inner and outer table, causing bone destruction and formation of granulation tissue. The extension of the infection through the diploe is resisted by proliferation of an encircling layer of concentrically placed fibroblasts and if the process is not arrested, extension then takes place through either tables.5 If the process is rapid, sequestration may occur; this appears as “bone sand” on radiography. Involvement of the outer table is usually associated with scalp swelling or a discharging sinus while involvement of the inner table results in extradural granulation tissue. The dura acts as a barrier to further spread, however intradural involvement is occasionally seen. A good immunity will cause slow and restricted evolution of the lesion, while decreased resistance will rapidly lead to subgaleal or extradural collections. Rare forms of presentation include seizures, motor deficits, meningitis, and non-specific headache as in our case.

A solitary discrete round or oval punched out osteolytic defect with minimal surrounding sclerosis in the frontoparietal bones is the commonest presentation of skull tuberculosis. When multiple they are of diffuse type with serpiginous and geographical defects of extensive bone loss.8 In our case, though an individual lytic lesion would have suggested a tuberculous aetiology, their multiplicity was unusual. There was no clinical or radiological evidence of involvement of surrounding soft tissue. Other investigations revealed no definitive evidence of an extracalvarial primary tuberculous focus. Thus a possibility of malignancy could not be ruled out without a histopathological diagnosis. A high index of suspicion and biopsy resulted in early diagnosis of this condition, before the adjacent soft tissues and the central nervous system were involved. Prompt treatment with antituberculous therapy resulted in cure and total regression of these lesions with no morbidity.

Final diagnosis

Calvarial tuberculosis presenting as multiple osteolytic lesions.

References

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